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Vaccines

Vaccines

JULI BERWALD

A vaccine is a medical preparation given to a person to provide immunity from a disease. Vaccines use a variety of different substances ranging from dead microorganisms to genetically engineered antigens to defend the body against potentially harmful antigens. Effective vaccines change the immune system by promoting the development of antibodies that can quickly and effectively attack disease causing microorganisms or viruses when they enter the body, preventing disease development.

Vaccine Development

The development of vaccines against diseases including polio, smallpox, tetanus, and measles is considered among one of the great accomplishments of medical science. Researchers are continually attempting to develop new vaccinations against other diseases. In particular, vigorous research into vaccines for Acquired Immune Deficiency Syndrome (AIDS), cancer and Severe Acute Respiratory Syndrome (SARS) is currently underway.

The first successful vaccine was developed from cowpox as a treatment for smallpox. Coined by Louis Pasteur (18221895), the etymology of the term vaccine reflects this achievement. It is taken from the Latin for cow (vacca ) and the word vaccinia, the virus that causes cowpox.

Smallpox. The first effective vaccine developed treated smallpox, a virulent disease that killed thousands of its victims and left thousands of others disfigured. In one of the first forms of inoculation, the ancient Chinese developed a snuff made from powdered smallpox scabs that was blown into the nostrils of uninfected individuals. Some individuals died from the therapy; however, in most cases, the mild infection produced offered protection from later, more serious infection.

In the late 1600s, European peasants employed a similar method of immunizing themselves against smallpox. In a practice referred to as "buying the smallpox," peasants in Poland, Scotland, and Denmark reportedly injected the smallpox virus under the skin to obtain immunity.

Lady Mary Wortley Montague, the wife of the British ambassador to Turkey brought information on immunization back to Europe in the early 1700s. Montague reported that the Turks injected a preparation of smallpox scabs into the veins of susceptible individuals. Those injected generally developed a mild case of smallpox from which they recovered rapidly. Montague convinced King George I to allow trials of the technique on inmates in Newgate Prison. Although some individuals died after receiving the injections, the trials were successful enough that variolation, or the direct injection of smallpox, became accepted medical practice. Variolation also was credited with protecting United States soldiers from smallpox during the Revolutionary War.

Edward Jenner (17491823), an English country physician, observed that people who were in contact with cows often developed cowpox, which caused pox sores but was not life threatening. Those people never developed smallpox. In 1796, Jenner tested the hypothesis that cowpox could be used to protect humans against smallpox. He injected a healthy eight-year-old boy with cowpox obtained from a milkmaid's sore. The boy was moderately ill and recovered. Jenner then injected the boy twice with the smallpox virus, and the boy did not get sick.

Modern knowledge of the immune system suggests that the virus that causes cowpox is similar enough to the virus that causes smallpox that the vaccine simulated an immune response to smallpox. Exposure to cowpox antigen stimulated the boy's immune system, producing cells that attacked the original antigen as well as the smallpox antigen. The vaccine also conditioned the immune system to produce antibodies more quickly and more efficiently against future infection by smallpox.

During the two centuries since its development, the smallpox vaccine gained popularity, protecting millions from contracting the disease. In 1979, following a major cooperative effort between nations and several international organizations, world health authorities declared smallpox the only infectious disease to be eradicated from the planet.

Rabies. In 1885 Louis Pasteur (18221895) saved the life of Joseph Meister, a nine year old who had been attacked by a rabid dog. Pasteur's series of experimental rabies vaccinations on the boy proved the effectiveness of the new vaccine.

Pasteur's rabies vaccine, the first human vaccine created in a laboratory, was made of an extract gathered from the spinal cords of rabies-infected rabbits. The live virus was weakened by drying over potash. The new vaccination was far from perfect, causing occasional fatalities and temporary paralysis. Individuals had to be injected 14 to 21 times.

The rabies vaccine has been refined many times. In the 1950s, a vaccine grown in duck embryos replaced the use of live virus, and in 1980, a vaccine developed in cultured human cells was produced. In 1998, the newest vaccine technologygenetically engineered vaccineswas applied to rabies. The new DNA vaccine cost a fraction of the regular vaccine. While only a few people die of rabies each year in the United States, more than 40,000 die worldwide, particularly in Asia and Africa. The less expensive vaccine will make vaccination far more available to people in less developed nations.

Polio. In the early 1900s polio was extremely virulent in the United States. At the peak of the epidemic, in 1952, polio killed 3,000 Americans, and 58,000 new cases of polio were reported.

In 1955 Jonas Salk (19141995) developed a vaccine for poliomyelitis. The Salk vaccine, a killed virus type, contained the three types of poliovirus that had been identified in the 1940s. In the first year the vaccine was distributed, dozens of cases of polio were reported in individuals who had received the vaccine or had contact with individuals who had been vaccinated. This resulted from an impure batch of vaccine that had not been completely inactivated. By the end of the incident, more than 200 cases had developed and 11 people had died.

In 1961, an oral polio vaccine developed by Albert B. Sabin (19061993) was licensed in the United States. The Sabin vaccine, which uses weakened, live polio viruses, quickly overtook the Salk vaccine in popularity in the United States, and is currently administered to all healthy children. Because it is taken orally, the Sabin vaccine is more convenient and less expensive to administer than the Salk vaccine.

Advocates of the Salk vaccine, which is still used extensively in Canada and many other countries, contend that it is safer than the Sabin oral vaccine. No individuals have developed polio from the Salk vaccine since the 1955 incident. In contrast, the Sabin vaccine has a very small but significant rate of complications, including the development of polio. However, there has not been one new case of polio in the United States since 1975, or in the Western Hemisphere since 1991. Though polio has not been completely eradicated, there were only 144 confirmed cases worldwide in 1999.

Influenza. Developing a vaccine against the influenza virus is problematic because the viruses that cause the flu constantly evolve. Scientists grapple with predicting what particular influenza strain will predominate in a given year. When the prediction is accurate, the vaccine is effective. When they are not, the vaccine is often of little help. However, the flu shot has had enough success that pediatricians are now recommending the vaccine for children older than 6 months.

AIDS Vaccine Research

Since the emergence of AIDS in the early 1980s, research for a treatment for the disease has resulted in clinical trials for more than 25 experimental vaccines. These range from whole-inactivated viruses to genetically engineered types. Some have focused on a therapeutic approach to help infected individuals to fend off further illness by stimulating components of the immune system; others have genetically engineered a protein on the surface of HIV to prompt immune response against the virus; and yet others attempted to protect uninfected individuals. The challenges in developing a protective vaccine include the fact that HIV appears to have multiple viral strains and mutates quickly.

In January 1999, a promising study was reported in Science magazine of a new AIDS vaccine created by injecting a healthy cell with DNA from a protein in the AIDS virus that is involved in the infection process. This cell was then injected with genetic material from cells involved in the immune response. Once injected into the individual, this vaccine "catches the AIDS virus in the act," exposing it to the immune system and triggering an immune response. This discovery offers considerable hope for development of an effective vaccine. As of April, 2003, a vaccine for AIDS had not been proven in clinical trials.

Cancer Vaccine Research

Stimulating the immune system is considered key by many researchers seeking a vaccine for cancer. Currently numerous clinical trials for cancer vaccines are in progress, with researchers developing experimental vaccines against cancer of the breast, colon, and lung, among others. Promising studies of vaccines made from the patient's own tumor cells and genetically engineered vaccines have been reported. Other experimental techniques attempt to penetrate the body in ways that could stimulate vigorous immune responses. These include using bacteria or viruses, both known to efficiently circulate through the body, as carriers of vaccine antigens. These bacteria or viruses could be treated or engineered to make them incapable of causing illness.

Vaccine Production

The classic methods for producing vaccines use biological products obtained directly from a virus or a bacteria. Depending on the vaccination, the virus or bacteria is either used in a weakened form, as in the Sabin oral polio vaccine; killed, as in the Salk polio vaccine; or taken apart so that a piece of the microorganism can be used. For example, the vaccine for Streptococcus pneumoniae, which causes pneumonia, uses bacterial polysaccharides, carbohydrates found in bacteria which contain large numbers of monosaccharides, a simple sugar. The different methods for producing vaccines vary in safety and efficiency. In general, vaccines that use live bacterial or viral products are extremely effective when they work, but carry a greater risk of causing disease. This is most threatening to individuals whose immune systems are weakened, such as individuals with leukemia. Children with leukemia are advised not to take the oral polio vaccine because they are at greater risk of developing the disease. Vaccines which do not include a live virus or bacteria tend to be safer, but their protection may not be as great.

The classic types of vaccines are all limited in their dependence on biological products, which often must be kept cold, may have a limited life, and can be difficult to produce. The development of recombinant vaccinesthose using chromosomal parts (or DNA) from a different organismhas generated hope for a new generation of man-made vaccines. The hepatitis B vaccine, one of the first recombinant vaccines to be approved for human use, is made using recombinant yeast cells genetically engineered to include the gene coding for the hepatitis B antigen. Because the vaccine contains the antigen, it is capable of stimulating antibody production against hepatitis B without the risk that live hepatitis B vaccine carries by introducing the virus into the blood stream.

DNA vaccines. As medical knowledge has increasedparticularly in the field of DNA vaccinesresearchers are working towards developing new vaccines for cancer, melanoma, AIDS, influenza, and numerous others. Since 1980, many improved vaccines have been approved, including several genetically engineered (recombinant) types which first developed during an experiment in 1990. These recombinant vaccines involve the use of so-called "naked DNA." Microscopic portions of a virus's DNA are injected into the patient. The patient's own cells then adopt that DNA, which is then duplicated when the cell divides, becoming part of each new cell. Researchers have reported success using this method in laboratory trials against influenza and malaria. These DNA vaccines work from inside the cell, not just from the cell's surface, as other vaccines do, allowing a stronger cell-mediated fight against the disease. Also, because the influenza virus constantly changes its surface proteins, the immune system or vaccines cannot change quickly enough to fight each new strain. However, DNA vaccines work on a core protein, which researchers believe should not be affected by these surface changes.

Vaccination programs. The Children's Vaccine Initiative, supported by the World Health Organization, the United Nations' Children's Fund, and other organizations, are working diligently to make vaccines easier to distribute in developing countries. More than four million people, mostly children, die every year from preventable diseases. Annually, measles kills 1.1 million children worldwide; whooping cough (pertussis) kills 350,000; hepatitis B 800,000; Haemophilus influenzae type b (Hib) 500,000; tetanus 500,000; rubella 300,000; and yellow fever 30,000. Another 8 million die from diseases for which vaccines are still being developed. These include pneumococcal pneumonia (1.2 million); acute respiratory virus infections (400,000), malaria (2 million); AIDS (2.3 million); and rotavirus (800,000). In August 1998, the Food and Drug Administration approved the first vaccine to prevent rotavirusa severe diarrhea and vomiting infection.

Effective vaccines have limited many of the life-threatening infectious diseases. In the United States, children starting kindergarten are required to be immunized against polio, diphtheria, tetanus, and several other diseases. Other vaccinations are used only by populations at risk, individuals exposed to disease, or when exposure to a disease is likely to occur due to travel to an area where the disease is common. These include influenza, yellow fever, typhoid, cholera, and Hepatitis A and B.

The measles epidemic of 1989 was a graphic display of the failure of many Americans to be properly immunized. A total of 18,000 people were infected, including 41 children who died after developing measles, an infectious, viral illness whose complications include pneumonia and encephalitis. The epidemic was particularly troubling because an effective, safe vaccine against measles has been widely distributed in the United States since the late 1960s. By 1991, the number of new measles cases had started to decrease, but health officials warned that measles remained a threat.

This outbreak reflected the limited reach of vaccination programs. Only 15% of the children between the ages of 16 and 59 months who developed measles between 1989 and 1991 had received the recommended measles vaccination. In many cases parents erroneously reasoned that they could avoid even the minimal risk of vaccine side effects "because all other children were vaccinated."

Nearly all children are immunized properly by the time they start school. However, very young children are far less likely to receive the proper vaccinations. Problems behind the lack of immunization range from the limited health care received by many Americans to the increasing cost of vaccinations. Health experts also contend that keeping up with a vaccine schedule, which requires repeated visits, may be too challenging for Americans who do not have a regular doctor or health provider.

Internationally, the challenge of vaccinating large numbers of people has also proven to be immense. Also, the reluctance of some parents to vaccinate their children due to potential side effects has limited vaccination use. Parents in the United States and several European countries have balked at vaccinating their children with the pertussis vaccine due to the development of neurological complications in a small number of children given the vaccine. Because of incomplete immunization, whooping cough remains common in the United States, with 30,000 cases and about 25 deaths due to complications annually. One response to such concerns has been testing in the United States of a new pertussis vaccine that has fewer side effects.

Vaccines against biological weapons. The United States Centers for Disease Control have identified six diseases that are the most likely to be used in biological weapons. They are smallpox, anthrax, plague, botulism, tularemia and viral hemorrhagic fevers. Vaccines against these diseases are in various stages of development and dissemination.

After smallpox was eradicated from the United States in 1972, vaccination against the disease was discontinued. As a result, there are a substantial number of people in the United States that have never been exposed to the virus. A majority of those vaccinated may have waning immunity because the smallpox vaccine provides a high level of immunity for approximately five years, with declining immunity thereafter. The United States has recently stockpiled enough vaccine to control an outbreak in case of a crisis, and plans are underway to increase vaccine production until stockpiles include enough vaccine to inoculate the entire U.S. population against smallpox.

Anthrax is of particular note as a biological weapon because it is an airborne pathogen that can be used in conjunction with traditional weapons. A vaccine against anthrax has recently been developed and it consists of a series of six subcutaneous injections. Because antibiotics are effective against the disease, the vaccine is currently only administered to populations at high risk, such as military personnel and researchers who handle the bacterium that causes anthrax.

Tularemia is caused by the bacterium Francisella tularensis, which is an extremely infectious airborne pathogen. Tularemia is usually treated with antibiotics, but a vaccine has been developed and the Food and Drug Administration is currently testing it. To date the vaccine has only been administered to laboratory workers who contact the pathogen on a regular basis.

Vaccines against several diseases that are of concern as biological weapons have not yet been developed. Plague is caused by a bacterium Yersina pestis that is often carried by rat mites. Although research is ongoing, there is no vaccine against this disease and one is unlikely to be developed for several years. Botulism is caused by a toxin produced by the bacterium Clostridium botulinum. Although an antitoxin that reduces the severity of the symptoms is available, there is no vaccine against botulism. Viral hemorrhagic fevers are caused by any one of several viruses including Ebola, Marburg, Lassa and Machupo. No vaccine against these pathogens is currently available.

FURTHER READING:

BOOKS:

Joellenbeck, L. M., L. L. Zwanziger, J. S. Durch, et al. The Anthrax Vaccine: Is It Safe? Does It Work? Washington, DC: National Academies Press, 2002.

Preston, R. The Demon in the Freezer. New York: Random House, 2002.

PERIODICALS:

Bradley, K. A., J. Mogridge, M. Mourey, et al. "Identification of the Cellular Receptor for Anthrax Toxin." Nature no. 414 (2001): 22529.

Friedlander, A. M. "Tackling Anthrax." Nature no. 414 (2001): 16061.

Henderson, D. A. "Smallpox: Clinical and Epidemiologic Features." Emerging Infectious Diseases no. 5 (1999): 53739.

Rosenthal, S. R., M. Merchlinsky, C. Kleppinger, et al. "Developing New Smallpox Vaccines." Emerging Infectious Diseases no. 7 (2001): 92026.

ELECTRONIC:

Centers for Disease Control and Prevention. "Smallpox Factsheet: Vaccine Overview." Public Health Emergency Preparedness and Response. December 9, 2002. <http://www.bt.cdc.gov/agent/smallpox/vaccination/facts.asp>(31 December 2002).

Rhode Island Department of Health: Bioterrorism Preparedness Program "History of Biological Warfare and Current Threat." <http://www.healthri.org/environment/biot/history.htm> (March 12, 2003).

SEE ALSO

Anthrax Vaccine
Biomedical Technologies
Biological Warfare
Pathogen Transmission
Surgeon General and Nuclear, Biological, and Chemical Defense, United States Office
Variola Virus

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Vaccine

Vaccine

A vaccine is a medical preparation given to provide immunity from a disease. Vaccines use a variety of different substances ranging from dead microorganisms to genetically engineered antigens to defend the body against potentially harmful microorganisms. Effective vaccines change the immune system by promoting the development of antibodies that can quickly and effectively attack a disease causing microorganism when it enters the body, preventing disease development.

The development of vaccines against diseases ranging from polio and smallpox to tetanus and measles is considered among one of the great accomplishments of medical science. Contemporary researchers are continually attempting to develop new vaccinations against such diseases as Acquired Immune Deficiency Syndrome (AIDS ), cancer, influenza , and other diseases.

Physicians have long observed that individuals who were exposed to an infectious disease and survived were somehow protected against that disease in the future. Prior to the invention of vaccines, however, infectious diseases swept through towns, villages, and cities with a horrifying vengeance.

The first effective vaccine was developed against smallpox, an international peril that killed thousands of its victims and left thousands of others permanently disfigured. The disease was so common in ancient China that newborns were not named until they survived the disease. The development of the vaccine in the late 1700s followed centuries of innovative efforts to fight smallpox.

The ancient Chinese were the first to develop an effective measure against smallpox. A snuff made from powdered smallpox scabs was blown into the nostrils of uninfected individuals. Some individuals died from the therapy; however, in most cases, the mild infection produced offered protection from later, more serious infection.

By the late 1600s, some European peasants employed a similar method of immunizing themselves against smallpox. In a practice referred to as "buying the smallpox," peasants in Poland, Scotland, and Denmark reportedly injected the smallpox virus into the skin to obtain immunity. At the time, conventional medical doctors in Europe relied solely on isolation and quarantine of people with the disease.

Changes in these practices took place, in part, through the vigorous effort of Lady Mary Wortley Montague , the wife of the British ambassador to Turkey in the early 1700s. Montague said the Turks injected a preparation of small pox scabs into the veins of susceptible individuals. Those injected generally developed a mild case of smallpox from which they recovered rapidly, Montague wrote.

Upon her return to Great Britain, Montague helped convince King George I to allow trials of the technique on inmates in Newgate Prison. Success of the trials cleared the way for variolation, or the direct injection of smallpox, to become accepted medical practice in England until a vaccination was developed later in the century. Variolation also was credited with protecting United States soldiers from smallpox during the Revolutionary War.

Regardless, doubts remained about the practice. Individuals were known to die after receiving the smallpox injections.

The next leap in the battle against smallpox occurred when Edward Jenner (17491823) acted on a hunch. Jenner observed that people who were in contact with cows often developed cowpox , which caused pox but was not life threatening. Those people did not develop smallpox. In 1796, Jenner decided to test his hypothesis that cowpox could be used to protect humans against smallpox. Jenner injected a healthy eight-year-old boy with cowpox obtained from a milkmaid's sore. The boy was moderately ill and recovered. Jenner then injected the boy twice with the smallpox virus, and the boy did not get sick.

Jenner's discovery launched a new era in medicine, one in which the intricacies of the immune system would become increasingly important. Contemporary knowledge suggests that cowpox was similar enough to smallpox that the antigen included in the vaccine stimulated an immune response to smallpox. Exposure to cowpox antigen transformed the boy's immune system, generating cells that would remember the original antigen. The smallpox vaccine, like the many others that would follow, carved a protective pattern in the immune system, one that conditioned the immune system to move faster and more efficiently against future infection by smallpox.

The term vaccination, taken from the Latin for cow (vacca ) was developed by Louis Pasteur (18221895) a century later to define Jenner's discovery. The term also drew from the word vaccinia, the virus drawn from cowpox and developed in the laboratory for use in the smallpox vaccine. In spite of Jenner's successful report, critics questioned the wisdom of using the vaccine, with some worrying that people injected with cowpox would develop animal characteristics, such as women growing animal hair. Nonetheless, the vaccine gained popularity, and replaced the more risky direct inoculation with smallpox. In 1979, following a major cooperative effort between nations and several international organizations, world health authorities declared smallpox the only infectious disease to be completely eliminated.

The concerns expressed by Jenner's contemporaries about the side effects of vaccines would continue to follow the pioneers of vaccine development. Virtually all vaccinations continue to have side effects, with some of these effects due to the inherent nature of the vaccine, some due to the potential for impurities in a manufactured product, and some due to the potential for human error in administering the vaccine.

Virtually all vaccines would also continue to attract intense public interest. This was demonstrated in 1885 when Louis Pasteur (18221895) saved the life of Joseph Meister, a nine year old who had been attacked by a rabid dog. Pasteur's series of experimental rabies vaccinations on the boy proved the effectiveness of the new vaccine.

Until development of the rabies vaccine, Pasteur had been criticized by the public, though his great discoveries included the development of the food preservation process called pasteurization . With the discovery of a rabies vaccine, Pasteur became an honored figure. In France, his birthday declared a national holiday, and streets renamed after him.

Pasteur's rabies vaccine, the first human vaccine created in a laboratory, was made of an extract gathered from the spinal cords of rabies-infected rabbits. The live virus was weakened by drying over potash. The new vaccination was far from perfect, causing occasional fatalities and temporary paralysis. Individuals had to be injected 1421 times.

The rabies vaccine has been refined many times. In the 1950s, a vaccine grown in duck embryos replaced the use of live virus, and in 1980, a vaccine developed in cultured human cells was produced. In 1998, the newest vaccine technologygenetically engineered vaccineswas applied to rabies. The new DNA vaccine cost a fraction of the regular vaccine. While only a few people die of rabies each year in the United States, more than 40,000 die worldwide, particularly in Asia and Africa. The less expensive vaccine will make vaccination far more available to people in less developed nations.

The story of the most celebrated vaccine in modern times, the polio vaccine, is one of discovery and revision. While the viruses that cause polio appear to have been present for centuries, the disease emerged to an unusual extent in the early 1900s. At the peak of the epidemic, in 1952, polio killed 3,000 Americans and 58,000 new cases of polio were reported. The crippling disease caused an epidemic of fear and illness as Americansand the worldsearched for an explanation of how the disease worked and how to protect their families.

The creation of a vaccine for poliomyelitis by Jonas Salk (19141995) in 1955 concluded decades of a drive to find a cure. The Salk vaccine, a killed virus type, contained the three types of polio virus which had been identified in the 1940s.

In 1955, the first year the vaccine was distributed, disaster struck. Dozens of cases were reported in individuals who had received the vaccine or had contact with individuals who had been vaccinated. The culprit was an impure batch of vaccine that had not been completely inactivated. By the end of the incident, more than 200 cases had developed and 11 people had died.

Production problems with the Salk vaccine were overcome following the 1955 disaster. Then in 1961, an oral polio vaccine developed by Albert B. Sabin (19061993) was licensed in the United States. The continuing controversy over the virtues of the Sabin and Salk vaccines is a reminder of the many complexities in evaluating the risks versus the benefits of vaccines.

The Sabin vaccine, which used weakened, live polio virus, quickly overtook the Salk vaccine in popularity in the United States, and is currently administered to all healthy children. Because it is taken orally, the Sabin vaccine is more convenient and less expensive to administer than the Salk vaccine.

Advocates of the Salk vaccine, which is still used extensively in Canada and many other countries, contend that it is safer than the Sabin oral vaccine. No individuals have developed polio from the Salk vaccine since the 1955 incident. In contrast, the Sabin vaccine has a very small but significant rate of complications, including the development of polio. However, there has not been one new case of polio in the United States since 1975, or in the Western Hemisphere since 1991. Though polio has not been completely eradicated, there were only 144 confirmed cases worldwide in 1999.

Effective vaccines have limited many of the life-threatening infectious diseases. In the United States, children starting kindergarten are required to be immunized against polio, diphtheria , tetanus, and several other diseases. Other vaccinations are used only by populations at risk, individuals exposed to disease, or when exposure to a disease is likely to occur due to travel to an area where the disease is common. These include influenza, yellow fever , typhoid, cholera, and Hepatitis A and B.

The influenza virus is one of the more problematic diseases because the viruses constantly change, making development of vaccines difficult. Scientists grapple with predicting what particular influenza strain will predominate in a given year. When the prediction is accurate, the vaccine is effective. When they are not, the vaccine is often of little help.

The classic methods for producing vaccines use biological products obtained directly from a virus or a bacteria . Depending on the vaccination, the virus or bacteria is either used in a weakened form, as in the Sabin oral polio vaccine; killed, as in the Salk polio vaccine; or taken apart so that a piece of the microorganism can be used. For example, the vaccine for Streptococcus pneumoniae uses bacterial polysaccharides, carbohydrates found in bacteria which contain large numbers of monosaccharides, a simple sugar. These classical methods vary in safety and efficiency. In general, vaccines that use live bacterial or viral products are extremely effective when they work, but carry a greater risk of causing disease. This is most threatening to individuals whose immune systems are weakened, such as individuals with leukemia. Children with leukemia are advised not to take the oral polio vaccine because they are at greater risk of developing the disease. Vaccines which do not include a live virus or bacteria tend to be safer, but their protection may not be as great.

The classical types of vaccines are all limited in their dependence on biological products, which often must be kept cold, may have a limited life, and can be difficult to produce. The development of recombinant vaccinesthose using chromosomal parts (or DNA) from a different organismhas generated hope for a new generation of man-made vaccines. The hepatitis B vaccine, one of the first recombinant vaccines to be approved for human use, is made using recombinant yeast cells genetically engineered to include the gene coding for the hepatitis B antigen. Because the vaccine contains the antigen, it is capable of stimulating antibody production against hepatitis B without the risk that live hepatitis B vaccine carries by introducing the virus into the blood stream.

As medical knowledge has increasedparticularly in the field of DNA vaccinesresearchers have set their sights on a wealth of possible new vaccines for cancer, melanoma, AIDS, influenza, and numerous others. Since 1980, many improved vaccines have been approved, including several genetically engineered (recombinant) types which first developed during an experiment in 1990. These recombinant vaccines involve the use of so-called "naked DNA." Microscopic portions of a viruses' DNA are injected into the patient. The patient's own cells then adopt that DNA, which is then duplicated when the cell divides, becoming part of each new cell. Researchers have reported success using this method in laboratory trials against influenza and malaria . These DNA vaccines work from inside the cell, not just from the cell's surface, as other vaccines do, allowing a stronger cell-mediated fight against the disease. Also, because the influenza virus constantly changes its surface proteins, the immune system or vaccines cannot change quickly enough to fight each new strain. However, DNA vaccines work on a core protein, which researchers believe should not be affected by these surface changes.

Since the emergence of AIDS in the early 1980s, a worldwide search against the disease has resulted in clinical trials for more than 25 experimental vaccines. These range from whole-inactivated viruses to genetically engineered types. Some have focused on a therapeutic approach to help infected individuals to fend off further illness by stimulating components of the immune system; others have genetically engineered a protein on the surface of HIV to prompt immune response against the virus; and yet others attempted to protect uninfected individuals. The challenges in developing a protective vaccine include the fact that HIV appears to have multiple viral strains and mutates quickly.

In January 1999, a promising study was reported in Science magazine of a new AIDS vaccine created by injecting a healthy cell with DNA from a protein in the AIDS virus that is involved in the infection process. This cell was then injected with genetic material from cells involved in the immune response. Once injected into the individual, this vaccine "catches the AIDS virus in the act," exposing it to the immune system and triggering an immune response. This discovery offers considerable hope for development of an effective vaccine. As of June 2002, a proven vaccine for AIDS had not yet been proven in clinical trials.

Stimulating the immune system is also considered key by many researchers seeking a vaccine for cancer. Currently numerous clinical trials for cancer vaccines are in progress, with researchers developing experimental vaccines against cancer of the breast, colon, and lung, among other areas. Promising studies of vaccines made from the patient's own tumor cells and genetically engineered vaccines have been reported. Other experimental techniques attempt to penetrate the body in ways that could stimulate vigorous immune responses. These include using bacteria or viruses, both known to be efficient travelers in the body, as carriers of vaccine antigens. Such bacteria or viruses would be treated or engineered to make them incapable of causing illness.

Current research also focuses on developing better vaccines. The Children's Vaccine Initiative, supported by the World Health Organization , the United Nation's Children's Fund, and other organizations, are working diligently to make vaccines easier to distribute in developing countries. Although more than 80% of the world's children were immunized by 1990, no new vaccines have been introduced extensively since then. More than four million people, mostly children, die needlessly every year from preventable diseases. Annually, measles kills 1.1 million children worldwide; whooping cough (pertussis ) kills 350,000; hepatitis B 800,000; Haemophilus influenzae type b (Hib) 500,000; tetanus 500,000; rubella 300,000; and yellow fever 30,000. Another 8 million die from diseases for which vaccines are still being developed. These include pneumococcal pneumonia (1.2 million); acute respiratory virus infections (400,000), malaria (2 million); AIDS (2.3 million); and rotavirus (800,000). In August, 1998, the Food and Drug Administration approved the first vaccine to prevent rotavirusa severe diarrhea and vomiting infection.

The measles epidemic of 1989 was a graphic display of the failure of many Americans to be properly immunized. A total of 18,000 people were infected, including 41 children who died after developing measles, an infectious, viral illness whose complications include pneumonia and encephalitis. The epidemic was particularly troubling because an effective, safe vaccine against measles has been widely distributed in the United States since the late 1960s. By 1991, the number of new measles cases had started to decrease, but health officials warned that measles remained a threat.

This outbreak reflected the limited reach of vaccination programs. Only 15% of the children between the ages of 16 and 59 months who developed measles between 1989 and 1991 had received the recommended measles vaccination. In many cases parent's erroneously reasoned that they could avoid even the minimal risk of vaccine side effects "because all other children were vaccinated."

Nearly all children are immunized properly by the time they start school. However, very young children are far less likely to receive the proper vaccinations. Problems behind the lack of immunization range from the limited health care received by many Americans to the increasing cost of vaccinations. Health experts also contend that keeping up with a vaccine schedule, which requires repeated visits, may be too challenging for Americans who do not have a regular doctor or health provider.

Internationally, the challenge of vaccinating large numbers of people has also proven to be immense. Also, the reluctance of some parents to vaccinate their children due to potential side effects has limited vaccination use. Parents in the United States and several European countries have balked at vaccinating their children with the pertussis vaccine due to the development of neurological complications in a small number of children given the vaccine. Because of incomplete immunization, whooping cough remains common in the United States, with 30,000 cases and about 25 deaths due to complications annually. One response to such concerns has been testing in the United States of a new pertussis vaccine that has fewer side effects.

Researchers look to genetic engineering, gene discovery, and other innovative technologies to produce new vaccines.

See also AIDS, recent advances in research and treatment; Antibody formation and kinetics; Bacteria and bacterial infection; Bioterrorism, protective measures; Immune stimulation, as a vaccine; Immunity, active, passive and delayed; Immunity, cell mediated; Immunity, humoral regulation; Immunochemistry; Immunogenetics; Immunologic therapies; Immunology; Interferon actions; Poliomyelitis and polio; Smallpox, eradication, storage, and potential use as a bacteriological weapon

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"Vaccine." World of Microbiology and Immunology. . Encyclopedia.com. 16 Aug. 2017 <http://www.encyclopedia.com>.

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Vaccines

Vaccines

Definition

A cancer vaccine is a method of treating the disease involving administration of one or more substances characteristic of the cancer, called antigens, often in combination with factors that boost immune function. This induces the patient's immune system to attack and eliminate the cancerous cells.

Purpose

Unlike traditional vaccines for infectious diseases, at this time cancer vaccines are not given to prevent the initial development of cancer. Instead, cancer vaccines are a method of treating cancer that has already occurred and are given to patients already diagnosed with cancer.

As a cancer treatment method, the ultimate goal of most cancer vaccines is the elimination of tumor or cancerous cells from the body. Other vaccines are given after the use of more traditional treatments, such as chemotherapy , radiation, or surgery, with the aim of suppressing the recurrence of the cancer.

Precautions

No vaccine has yet been approved by the Food and Drug Administration (FDA) for the treatment of cancer. Accordingly, vaccines are not standard treatments and other more traditional treatments should be investigated first. Vaccines are available only through participation in clinical trials . Each trial has its own criteria that can limit who can participate. However, many cancers have a current trial for one or more types of vaccines. The American Society for Gene Therapy states that as of late 2000, vaccines were the most common approach to gene therapy being studied by researchers.

Most vaccine trials test the response of the disease with and without the vaccine or the effect of substances added to the vaccine, called adjuvants. Such trials usually only accept patients that have already tried the standard treatment methods. Others test a standard treatment method with and without the addition of the vaccine. A very few compare the standard treatment to the vaccine.

Looking at cancer vaccines overall, this treatment method has been more successful eliminating very small tumors rather than the getting rid of a large tumor load. So if the size of the tumor is significant, a more realistic goal is to shrink the tumor and reduce its effect on the patient's body, rather than total elimination of the cancer.

The complexity of the human immune system has made it very difficult to develop an effective vaccine. Tumors have strategies to evade detection by the immune system. Most notably, they mimic the outward appearance and antigens of the body's own cells. The immune system's built-in lack of response against "self" allows the tumor to escape notice by the body. Now fully aware of this phenomenon, researchers are working to develop methods of circumventing this problem to develop a highly effective vaccine system.

Description

There are three general types of cancer vaccines, those that use whole tumor cells, those that use only one or more substances derived from the tumors, or those that administer primed cells from the patient's immune system.

Whole cell vaccines

Whole cell vaccines are autologous when they contain only inactivated tumor cells from the patient's own tumors. The cells have been isolated from the tumor and made to grow in the laboratory, a process known as creating a cell line. Allogeneic whole cell vaccines are made from inactivated tumor cells isolated from one or more other people. The main advantage to autologous vaccines is the direct relation between the vaccine and the tumor target. However, because of the screening of self antigens away from a body's own immune system, immune response to tumor antigens in autologous whole cells vaccines can be low.

Allogeneic vaccines avoid some of the problems of autologous vaccines. First, cell lines do not have to be created for each patient, a labor-intensive process that can have highly variable results. Second, the same vaccine can be given to all patients, making the response to the vaccine more predictable. Third, a use of a pool of tumor cells can increase the possibility of having the full repertoire of the tumor antigens in the vaccine. This helps to overcome the ability of tumor cells to escape notice by the immune system. Finally, by using well-characterized cell lines, it is much easier for the researcher to add genetic modifications that increase the immune system's response to the cells.

Isolated antigen vaccines

There are many kinds of vaccines that deliver only a portion of the tumor cell that will elicit an immune response, called an antigen. Some antigens are unique to a cancer type, some are unique to an individual tumor, while a very few are found in more than one cancer type. For example, vaccines against telomerase and human chorionic gonadotripin (hCG), two proteins produced by many cancers, have been developed, raising hopes for the development of a universal cancer vaccine.

The most common kind of antigen used in cancer vaccines is a protein or a part of a protein. The protein can actually be isolated from the tumor cells, or more commonly, produced in large quantity using genetic engineering techniques. When a part of a protein is used, experimental efforts generally preceded the vaccine production to determine what parts of the protein were often the target of immune responses. Parts of proteins that elicit immune responses are called epitopes.

Antigens do not necessarily have to be proteins. Immune responses are also mounted against the carbohydrate (sugar) molecules present on the surface of the proteins. Tumor proteins can have unusual carbohydrate structures that set them apart from cells from normal tissue. Carbohydrates are also found in abundant numbers on the surface of the tumor cells. Accordingly, researchers have developed cancer vaccines that combine the tumor-characteristic carbohydrates anchored on protein bases. These vaccines are being tested for their ability to reduce the recurrence of prostate cancer .

Vaccines can also contain the naked genetic material encoding the protein (either deoxyribose nucleic acid, DNA, or ribose nucleic acid, RNA). After the genetic material gains entry to the cell, the cellular machinery uses it to produce the antigen and an immune response is mounted against it. Animal studies have found that these types of vaccines are very dependent on the particular antigen and the mode of administration of the vaccine. A unique method of delivery used with DNA or RNA vaccines is the coating of tiny gold beads with the genetic material and shooting the beads into the skin.

Genetically engineered viruses can also be used to bring the DNA or RNA into the cell. When used in this way the viruses are called viral vectors. One example of a viral vector currently being used as a cancer vaccine is one based on the adenovirus. When viruses are used as vectors they have been altered to no longer cause disease, but they do retain the ability to infect human cells. Instead of making new viruses, the infected cells make the desired antigen, and the body will respond against it. Viral vectors can also carry the genetic instructions for factors, called cytokines, which boost the immune system's response to the antigen.

Antigen-presenting cell (APC) vaccines

Vaccines can also be made that contain cells from the patient's own immune system, in particular APCs (antigen-presenting cells). These cells play a central role in the development of an immune response against a particular antigen. Specifically, APCs ingest the antigen and present them to the T cells, a type of immune cells responsible for targeting and killing cells seen as foreign to the body. If T cells are exposed to the antigen by an APC, as opposed to seeing the antigen on the cell itself, they are more strongly activated. That is, more T cells that specifically attack that antigen are produced and the immune response against the foreign cell is stronger.

Dendritic cells are a type of APC that is most effective in activating T cells. For this reason, they are often the kind of cells used in APC vaccines. Unfortunately, the number of dendritic cells circulating in the blood at any one time is relatively low. However, new techniques have been developed that allow that small number of dendritic cells to be isolated and then stimulated outside the body to result in a usable number. During stimulation, the dendritic cells are exposed to the tumor antigen, a process known as priming. Thus, when injected into the body, the dendritic cells are primed to recruit large numbers of T cells specific against the tumor antigen.

Cyokines and adjuvants

Because of the ability of tumor cells to escape detection by the immune system, an important component of many cancer vaccines is the addition of biological factors or chemical adjuvants to help boost immune response. One type of adjuvant is a cytokine, a factor normally produced by cells of the immune system to help recruit cells to the site of the foreign cells or help T cells function. Some examples of cytokines used in vaccines are granulocyte/macrophage colony stimulating factor (GM-CSF, or sargramostim ), the interleukins (especially IL-2), the interferons (INFs), and tumor necrosis factor alpha (TNF-).

Adjuvants are chemical additions to vaccines that help boost the response to the contained cells or antigens. Adjuvants are derived from a variety of sources and can be isolated from animals, plants, or are synthetic chemical compounds. Several adjuvants in use with cancer vaccines are keyhole lympocianin (KLH, derived from shell-dwelling sea animals), incomplete Freud's adjuvant (IFA, mineral oil and an emulsifying agent), and QS-21 (a chemical derived from the soapbark tree).

Administration

The particular administration method and schedule will vary from clinical trial to clinical trial. Administration methods can include intradural (injection within the skin), subcutaneous (injection below the skin), injection into the lymph nodes, or intravenous (injection into the veins). Typically, vaccines are administered as a series of several doses (initial challenge and boosters). Many clinical trials utilize various administration methods and timing strategies in order to try to determine the best means of inducing an anti-tumor immune response.

Preparation

Before enrolling in a clinical trial, patients should discuss the potential benefits and risks with their doctor. Clinical trials can be located by contacting the research institutes directly or by searching the Internet. A particularly good site for getting information about clinical trials for cancer treatment is run by the National Cancer Institute (<http://www.clincialtrials.gov>).

Aftercare

One of the most striking advantages of vaccines compared to other cancer treatments is the relatively low incidence of side effects. Particularly if IFN is used as an immunoadjuvant, patients sometimes experience flu-like symptoms. However, other than some soreness at the site of injection, vaccine patients generally have no adverse reactions to this kind of treatment.

Risks

The greatest risk with cancer vaccines is that there will be no immune response and the treatment will be ineffective. Although serious adverse reactions to the antigens, such as the attack of healthy cells, are theoretically possible, these fears have not materialized. Other than some mild adverse reactions, such as fever and redness of the skin at the injection site, vaccine treatment appears relatively low-risk in the traditional sense.

Normal results

Based on a review of published clinical trials as of 2000, normal results for this treatment is, unfortunately, little or no effect. Although a response by the immunized patient's T cells against the tumor is often documented by testing, the effect on disease is generally marginal. These results could be at least partially due to the selection process for patients in the trials, who are often suffering from late-stage cancers.

Abnormal results

For each trial, there are a small percentage of patients who have complete, partial, or mixed response to the vaccine. Others show a stabilization of the disease where deterioration of condition would be expected. As traditional treatments were often unsuccessful with these patients, these results are significant. However, the very low rate of success underscores the complexity of the human immune system, the number of variables in the vaccine method, and the amount of research that will need to be done to develop an effective vaccine treatment for this disease.

See Also Monoclonal antibodies; Immunologic therapy

Resources

BOOKS

Restifo, Nicholas, et al. "Therapeutic Cancer Vaccines." InCancer Principles & Practice of Oncology, edited by DeVita, Vincent T., et al. Philadelphia: LippincottWilliams & Wilkins, 2001, pp. 3195-217.

PERIODICALS

Bocchia, Monica, et al. "Antitumor Vaccination: Where WeStand." Haematologica 85 (November 2000): 1172-206.

Monzavi-Karbassi, B., and T. Kieber-Emmons. "Current concepts in cancer vaccine strategies." Biotechniques 30 (January 2001): 170.

OTHER

"First Potential Universal Cancer Vaccine Shows Promise InLab." Science Daily Magazine. 30 August 2000. 12 April 2001. 28 June 2001 <http://www.sciencedaily.com/print/2000/08/000830073711.htm>.

"Treating Cancer with Vaccine Therapy." Cancer Trials. July 20, 1999. 12 April 2001. 28 June 2001.<http://cancertrials.nci.nih.gov/news/features/vaccine/index.html>.

Michelle Johnson, M.S., J.D.

KEY TERMS

Adjuvant

A substance added to a vaccine to increase the immune system's response to the vaccine contents.

Allogeneic

A type of vaccine made up of tumor cells derived from persons other than the patient.

Antigen

A substance characteristic of a tumor that evokes an immune response.

Antigen presenting cell

A cell of the immune system that ingests antigens and exposes them to cells of the immune system in a way that activates the cells to seek out and destroy any other cells displaying that antigen.

Autologous

A type of vaccine made up of tumor cells from the patient's own tumor.

Cytokine

A substance made by cells of the immune system that increases the response to a foreign substance.

Dendritic cell

A special type of antigen-presenting cell that is effective in stimulating T cells.

Epitope

A portion of a protein or other molecule that is the specific target of an immune response.

QUESTIONS TO ASK THE DOCTOR

  • Have all the standard treatment methods for my cancer been tried?
  • Is there a vaccine in clinical trials for my kind of cancer?
  • Do I fulfill the requirements necessary for the clinical trial for this vaccine?
  • Has this vaccine been tried on human patients before?
  • If so, what were the results?

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Vaccines

Vaccines

Investigations of the circumstances surrounding an illness outbreak can be a valuable means of determining how an infection is spread, its natural reservoirs, and in identifying subpopulations that display immunity to the infection. These forensic investigations can aid in the development of protective measures. Principle among protective measures are vaccines.

A vaccine is a medical preparation given to a person to provide immunity from a disease. Vaccines use a variety of different substances ranging from dead microorganisms to genetically engineered antigens to defend the body against potentially harmful antigens. Effective vaccines change the immune system by promoting the development of antibodies that can quickly and effectively attack disease causing microorganisms or viruses when they enter the body, preventing disease development.

The development of vaccines against diseases including polio, smallpox , tetanus, and measles is considered among the great accomplishments of medical science. Researchers are continually attempting to develop new vaccinations against other diseases. In particular, vigorous research into vaccines for acquired immune deficiency syndrome (AIDS), some cancer, severe acute respiratory syndrome (SARS), and avian influenza is currently underway.

The first successful vaccine was developed from cowpox as a treatment for smallpox. Coined by Louis Pasteur (18221895), the etymology of the term vaccine reflects this achievement. It is taken from the Latin for cow (vacca ) and the word vaccinia, the virus that causes cowpox.

This first effective vaccine developed treated smallpox, a virulent disease that killed thousands of its victims and left thousands of others disfigured. In one of the first forms of inoculation, ancient Chinese people developed a snuff made from powdered smallpox scabs that was blown into the nostrils of uninfected individuals. Some individuals died from the therapy; however, in most cases, the mild infection produced offered protection from later, more serious infection.

In the late 1600s, European peasants employed a similar method of immunizing themselves against smallpox. In a practice referred to as "buying the smallpox," peasants in Poland, Scotland, and Denmark reportedly injected the smallpox virus under the skin to obtain immunity.

Lady Mary Wortley Montagu, the wife of the British ambassador to Turkey, brought information on immunization back to Europe in the early 1700s. Montague reported that the Turks injected a preparation of small pox scabs into the veins of susceptible individuals. Those injected generally developed a mild case of smallpox from which they recovered rapidly. Montague convinced King George I to allow trials of the technique on inmates in Newgate Prison. Although some individuals died after receiving the injections, the trials were successful enough that variolation, or the direct injection of smallpox, became accepted medical practice. Variolation also was credited with protecting United States soldiers from smallpox during the Revolutionary War.

Edward Jenner (17491823), an English country physician, observed that people who were in contact with cows often developed cowpox, which caused pox sores but was not life threatening. Those people never developed smallpox. In 1796 Jenner tested the hypothesis that cowpox could be used to protect humans against smallpox. He injected a healthy eight-year-old boy with cowpox obtained from a milkmaid's sore. The boy was moderately ill and recovered. Jenner then injected the boy twice with the smallpox virus, and the boy did not get sick.

Modern knowledge of the immune system suggests that the virus that causes cowpox is similar enough to the virus that causes smallpox that the vaccine simulated an immune response to smallpox. Exposure to cowpox antigen stimulated the boy's immune system, producing cells that attacked the original antigen as well as the smallpox antigen. The vaccine also conditioned the immune system to produce antibodies more quickly and more efficiently against future infection by smallpox.

During the two centuries since its development, the smallpox vaccine gained popularity, protecting millions from contracting the disease. In 1979, following a major cooperative effort between nations and several international organizations, world health authorities declared smallpox the only infectious disease to be eradicated from the planet.

In 1885 Louis Pasteur (18221895) saved the life of Joseph Meister, a nine year old who had been attacked by a rabid dog. Pasteur's series of experimental rabies vaccinations on the boy proved the effectiveness of the new vaccine.

Pasteur's rabies vaccine, the first human vaccine created in a laboratory, was made of an extract gathered from the spinal cords of rabies-infected rabbits. The live virus was weakened by drying over potash. The new vaccination was far from perfect, causing occasional fatalities and temporary paralysis. Individuals had to be injected 14 to 21 times.

The rabies vaccine has been refined many times. In the 1950s, a vaccine grown in duck embryos replaced the use of live virus, and in 1980, a vaccine developed in cultured human cells was produced. In 1998, the newest vaccine technologygenetically engineered vaccineswas applied to rabies. The new DNA vaccine cost a fraction of the regular vaccine. While only a few people die of rabies each year in the United States, more than 40,000 die worldwide, particularly in Asia and Africa. The less expensive vaccine will make vaccination far more available to people in less developed nations.

In the early 1900s polio was extremely virulent in the United States. At the peak of the epidemic, in 1952, polio killed 3,000 Americans, and 58,000 new cases of polio were reported.

In 1955 Jonas Salk (19141995) developed a vaccine for poliomyelitis. The Salk vaccine, a killed virus type, contained the three types of poliovirus that had been identified in the 1940s. In the first year the vaccine was distributed, dozens of cases of polio were reported in individuals who had received the vaccine or had contact with individuals who had been vaccinated. This resulted from an impure batch of vaccine that had not been completely inactivated. By the end of the incident, more than 200 cases had developed and 11 people had died.

In 1961, an oral polio vaccine developed by Albert B. Sabin (19061993) was licensed in the United States. The Sabin vaccine, which uses weakened, live polio viruses, quickly overtook the Salk vaccine in popularity in the United States, and is currently administered to all healthy children. Because it is taken orally, the Sabin vaccine is more convenient and less expensive to administer than the Salk vaccine.

Advocates of the Salk vaccine, which is still used extensively in Canada and many other countries, contend that it is safer than the Sabin oral vaccine. No individuals have developed polio from the Salk vaccine since the 1955 incident. In contrast, the Sabin vaccine has a very small, but significant, rate of complications, including the development of polio. However, there has not been one new case of polio in the United States since 1975, or in the Western Hemisphere since 1991. Although polio has not been completely eradicated, there were only 144 confirmed cases worldwide in 1999.

Developing a vaccine against the influenza virus is problematic because the viruses that cause the flu constantly evolve. Scientists grapple with predicting what particular influenza strain will predominate in a given year. When the prediction is accurate, the vaccine is effective. When they are not, the vaccine is often of little help. However, the flu shot has had enough success that pediatricians are now recommending the vaccine for children older than six months.

Since the emergence of AIDS in the early 1980s, research for a treatment for the disease has resulted in clinical trials for more than 25 experimental vaccines. These range from whole-inactivated viruses to genetically engineered types. Some have focused on a therapeutic approach to help infected individuals to fend off further illness by stimulating components of the immune system. Others have genetically engineered a protein on the surface of HIV to prompt immune response against the virus; and yet others attempted to protect uninfected individuals. The challenges in developing a protective vaccine include the fact that HIV appears to have multiple viral strains and mutates quickly.

In January, 1999, a promising study was reported in Science magazine of a new AIDS vaccine created by injecting a healthy cell with DNA from a protein in the AIDS virus that is involved in the infection process. This cell was then injected with genetic material from cells involved in the immune response. Once injected into the individual, this vaccine "catches the AIDS virus in the act," exposing it to the immune system and triggering an immune response. This discovery offers considerable hope for development of an effective vaccine. As of 2005, a vaccine for AIDS had not been proven in clinical trials.

Stimulating the immune system is considered key by many researchers seeking a vaccine for cancer. Currently numerous clinical trials for cancer vaccines are in progress, with researchers developing experimental vaccines against cancer of the breast, colon, and lung, among others. Promising studies of vaccines made from the patient's own tumor cells and genetically engineered vaccines have been reported. Other experimental techniques attempt to penetrate the body in ways that could stimulate vigorous immune responses. These include using bacteria or viruses, both known to efficiently circulate through the body, as carriers of vaccine antigens. These bacteria or viruses could be treated or engineered to make them incapable of causing illness.

The classic methods for producing vaccines use biological products obtained directly from a virus or a bacteria. Depending on the vaccination, the virus or bacteria is either used in a weakened form, as in the Sabin oral polio vaccine; killed, as in the Salk polio vaccine; or taken apart so that a piece of the microorganism can be used. For example, the vaccine for Streptococcus pneumoniae, which causes pneumonia, uses bacterial polysaccharides, carbohydrates found in bacteria which contain large numbers of monosaccharides, a simple sugar. The different methods for producing vaccines vary in safety and efficiency. In general, vaccines that use live bacterial or viral products are extremely effective when they work, but carry a greater risk of causing disease. This is most threatening to individuals whose immune systems are weakened, such as individuals with leukemia. Children with leukemia are advised not to take the oral polio vaccine because they are at greater risk of developing the disease. Vaccines which do not include a live virus or bacteria tend to be safer, but their protection may not be as great.

The classical types of vaccines are all limited in their dependence on biological products, which often must be kept cold, may have a limited life, and can be difficult to produce. The development of recombinant vaccinesthose using chromosomal parts (or DNA) from a different organismhas generated hope for a new generation of man-made vaccines. The hepatitis B vaccine, one of the first recombinant vaccines to be approved for human use, is made using recombinant yeast cells genetically engineered to include the gene coding for the hepatitis B antigen. Because the vaccine contains the antigen, it is capable of stimulating antibody production against hepatitis B without the risk that live hepatitis B vaccine carries by introducing the virus into the blood stream.

As medical knowledge has increasedparticularly in the field of DNA vaccinesresearchers are working toward developing new vaccines for cancer, melanoma, AIDS, influenza, and numerous others illnesses. Since 1980, many improved vaccines have been approved, including several genetically engineered (recombinant) types which first developed during an experiment in 1990. These recombinant vaccines involve the use of so-called "naked DNA." Microscopic portions of a viruses's DNA are injected into the patient. The patient's own cells then adopt that DNA, which is then duplicated when the cell divides, becoming part of each new cell. Researchers have reported success using this method in laboratory trials against influenza and malaria. These DNA vaccines work from inside the cell, not just from the cell's surface, as other vaccines do, allowing a stronger cell-mediated fight against the disease. Also, because the influenza virus constantly changes its surface proteins, the immune system or vaccines cannot change quickly enough to fight each new strain. However, DNA vaccines work on a core protein, which researchers believe should not be affected by these surface changes.

The measles epidemic of 1989 was a graphic display of the failure of many Americans to be properly immunized. A total of 18,000 people were infected, including 41 children who died after developing measles, an infectious, viral illness whose complications include pneumonia and encephalitis. The epidemic was particularly troubling because an effective, safe vaccine against measles has been widely distributed in the United States since the late 1960s. By 1991, the number of new measles cases had started to decrease, but health officials warned that measles remained a threat.

see also Pathogens; United States Army Medical Research Institute of Infectious Diseases (USAMRIID).

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Vaccine

Vaccine

Background

The development of vaccines to protect against viral disease is one of the hallmarks of modern medicine. The first vaccine was produced by Edward Jenner in 1796 in an attempt to provide protection against smallpox. Jenner noticed that milkmaids who had contracted cowpox, a relatively innocuous infection, seemed to be resistant to smallpox, a disease of humans that regularly reached epidemic levels with extremely high mortality rates.

Jenner theorized (correctly) that cowpox, a disease of animals, was similar to smallpox. He concluded that the human reaction to an injection of cowpox virus would somehow teach the human body to respond to both viruses, without causing major illness or death. Today, smallpox is totally eradicated. Only two frozen samples of this virulent virus exist (one in the United States, the other in Russia), and as of mid-1995 there is serious scientific debate about whether to destroy the samples, or keep them for further laboratory study.

A virus is a small bit of RNA (Ribonucleic acid) and/or DNA (deoxyribonucleic acid), the material in all living cells that instructs the cell how to grow and reproduce. Viruses cannot reproduce by themselves, but only by taking over the nucleus of a host cell and instructing the cell to make additional viruses. When a virus successfully invades an organism, it takes over the cell growth process in the host.

Under ordinary circumstances, the human body responds to viral invasion in several different ways. Generalized immunity to a virus can be developed by the cells in the body that are targets of viral invasion. In this situation, viruses are prevented from gaining access to host cells. A more common protection is the body's ability to develop blood and lymph cells that destroy or limit the efficacy of the invading virus. Often, an infected human body will "leam" how to respond to a specific virus in the future, so that a single infection, especially from a relatively benign virus, usually teaches the body how to respond to additional invasions from the same virus. The common cold, for example, is caused by one of several hundred viruses. After recovering from a cold, most people are resistant to the particular virus that caused the particular cold, although similar cold viruses will still cause similar or identical symptoms. For some innocuous viruses, a person might even develop immunity without becoming visibly ill.

Virus Families

There are usually several variations or strains of any particular virus. Depending on the number of varieties, a biologist might group viruses as types or strains. Vaccines frequently are made from more than one group of related viruses; a preventive reaction to the multivalent vaccination will probably cause immunity to almost all of the group's variants, or at least to those variants which a person is likely to encounter. Choice of the specific members of the group to use in a vaccine are made with painstaking care and deliberation.

The Manufacturing
Process

Manufacturing an anti-virus vaccine today is a complicated process even after the arduous task of creating a potential vaccine in the laboratory. The change from manufacturing a potential vaccine in small quantities to manufacturing gallons of safe vaccine in a production situation is dramatic, and simple laboratory procedure may not be amenable to a "scale up" situation.

The Seed

  • 1 Manufacturing begins with small amounts of a specific virus (or seed). The virus must be free of impurities, including other similar viruses and even variations of the same type of virus. Additionally, the seed must be kept under "ideal" conditions, usually frozen, that prevent the virus from becoming either stronger or weaker than desired. Stored in small glass or plastic containers, amounts as small as only 5 or 10 cubic centimeters, but containing thousands if not millions of viruses, will eventually lead to several hundred liters of vaccine. Freezers are maintained at specified temperatures; charts and/or dials outside of the freezer keep a continuous record of the temperature. Sensors will set off audible alarm signals and/or computer alarms if the freezer temperature goes out of range.

Growing the virus

  • 2 After defrosting and warming the seed virus under carefully specified conditions (i.e., at room temperature or in a water bath), the small amount of virus cells is placed into a "cell factory," a small machine that, with the addition of an appropriate medium, allows the virus cells to multiply. Each type of virus grows best in a medium specific to it, established in pre-manufacturing laboratory procedures, but all contain proteins from mammals in one form or another, such as purified protein from cow blood. The medium also contains other proteins and organic compounds that encourage the reproduction of the virus cells. As far as the virus is concerned, the medium in a cell factory is a host for reproduction. Mixed with the appropriate medium, at appropriate temperature, and with a predetermined amount of time, viruses will multiply.
  • 3 In addition to temperature, other factors must be monitored, including the pH of the mixture. pH is a measure of acidity or basicity, measured on a scale from 0 to 14, and the viruses must be kept at a defined pH within the cell factory. Plain water, which is neither acidic or basic (neutral) has a pH of 7. Although the container in which the cells are growing is not very large (perhaps the size of a 4-8 quart pot), there are an impressive number of valves, tubes, and sensors connected to it. Sensors monitor pH and temperature, and there are various connections for adding media or chemicals such as oxygen to maintain the pH, places to withdraw samples for microscopic analysis, and sterile arrangements for adding the components of the cell factory and withdrawing the intermediate product when it is ready.
  • 4 The virus from the cell factory is then separated from the medium, and placed in a second medium for additional growth. Early methods of 40 or 50 years ago used a bottle to hold the mixture, and the resulting growth was a single layer of viruses floating on the medium. It was soon discovered that if the bottle was turned while the viruses were growing, even more virus could be produced because a layer of virus grew on all inside surfaces of the bottle. An important discovery in the 1940s was that cell growth is greatly stimulated by the addition of enzymes to a medium, the most commonly used of which is trypsin. An enzyme is a protein that also functions as a catalyst in the feeding and growth of cells.

    In current practice, bottles are not used at all. The growing virus is kept in a container larger than but similar to the cell factory, and mixed with "beads," near microscopic particles to which the viruses can attach themselves. The use of the beads provides the virus with a much greater area to attach themselves to, and consequently, a much greater growth of virus. As in the cell factory, temperature and pH are strictly controlled. Time spent in growing virus varies according to the type of virus being produced, and is, in each case, a closely guarded secret of the manufacturer.

Separation

  • 5 When there is a sufficient number of viruses, they are separated from the beads in one or more ways. The broth might be forced through a filter with openings large enough to allow the viruses to pass through, but small enough to prevent the beads from passing. The mixture might be centrifuged several times to separate the virus from the beads in a container from which they can then be drawn off. Still another alternative might be to flood the bead mixture with another medium which washes the virus off the beads.

Selecting the strain

The eventual vaccine will be either made of attenuated (weakened) virus, or a killed virus. The choice of one or the other depends on a number of factors including the efficacy of the resulting vaccine, and its secondary effects. Ru vaccine, which is developed almost every year in response to new variants of the causative virus, is always an attenuated vaccine. The virulence of a virus can dictate the choice; rabies vaccine, for example, is always a killed vaccine.

  • 6 If the vaccine is attenuated, the virus is usually attenuated before it goes through the production process. Carefully selected strains are cultured (grown) repeatedly in various media. There are strains of viruses that actually become stronger as they grow. These strains are clearly unusable for an attenuated vaccine. Other strains become too weak as they are cultured repeatedly, and these too are unacceptable for vaccine use. Like the porridge, chair, and bed that Goldilocks liked, only some viruses are "just right," reaching a level of attenuation that makes them acceptable for vaccine use, and not changing in strength. Recent molecular technology has made possible the attenuation of live virus by molecular manipulation, but this method is still rare.
  • 7 The virus is then separated from the medium in which it has been grown. Vaccines which are of several types (as most are) are combined before packaging. The actual amount of vaccine given to a patient will be relatively small compared with the medium in which it is given. Decisions about whether to use water, alcohol, or some other solution for an injectable vaccine, for example, are made after repeated tests for safety, sterility, and stability.

Quality Control

To protect both the purity of the vaccine and the safety of the workers who make and package the vaccine, conditions of laboratory cleanliness are observed throughout the procedure. All transfers of virus and media are conducted under sterile conditions, and all instruments used are sterilized in an autoclave (a machine that kills organisms by heat, and which may be as small as a jewel box or as large as an elevator) before and after use. Workers performing the procedures wear protective clothing which includes disposable tyvek gowns, gloves, booties, hair nets, and face masks. The manufacturing rooms themselves are specially air conditioned so that there is a minimal number of particles in the air.

The Approval Process

In order for prescription drugs to be sold in the United States, a drug manufacturer must meet strict licensing requirements established by law and enforced by the Food and Drug Administration (FDA).

All prescription drugs must undergo three phases of testing, although data from the second phase can sometimes be used to meet third phase requirements. Phase 1 testing must prove that a medicine is safe, or at least that no untoward or unexpected effects will occur from its administration. If a medicine passes Phase I testing, it must next be tested for efficacyit must do what it is supposed to do; medicine cannot be sold that is useless, or that makes claims for an effect that it does not have. Finally, Phase III testing is designed to quantify the effectiveness of a medicine or drug. Although vaccines are expected to have effectiveness close to 100%, certain medicines might well be acceptable even if they have limited effectiveness, as long as the prescribing physician knows the odds.

The entire manufacturing process is reviewed carefully by the FDA which examines records of procedures as well as visiting the manufacturing site itself. Each step in the manufacturing process must be documented, and the manufacturer must demonstrate a "state of control" for the manufacturing process. This means that scrupulous records must be kept for every step in the process, and there must be written instructions for each step of the process. Except in cases of grievous error, the FDA does not determine if each step in a process is correct, but only that it is safe and is documented sufficiently to be performed as the manufacturer stipulates.

The Future

Producing a usable, safe antiviral vaccine involves a large number of steps which, unfortunately, cannot always be done for each and every virus. There is still much to be done and learned. The new methods of molecular manipulation have caused more than one scientist to believe that the vaccine technology is only now entering a "golden age." Refinements of existing vaccines are possible in the future. Rabies vaccine, for example, produces side effects which make the vaccine unsatisfactory for mass immunization; in the United States, rabies vaccine is now used only on patients who have contracted the virus from an infected animal and are likely, without immunization, to develop the fatal disease.

The HIV virus, which biologists believe causes AIDS, is not currently amenable to traditional vaccine production methods. The AIDS virus rapidly mutates from one strain to another, and any given strain does not seem to confer immunity against other strains. Additionally, a limited, immunizing effect of either attenuated or killed virus cannot be demonstrated in either the laboratory or in test animals. No HIV vaccine has yet been developed.

Where To Learn More

Books

Dulbecco, Renato and Harold S. Ginsberg. Virology. 2nd edition. J.B. Lippincott Company, 1988.

Plotkin, Stanley A. and Edward A. Mortimer, Jr., eds. Vaccines. W.B. Saunders Company, 1988.

Lawrence H. Berlow

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Vaccine

Vaccine

A vaccine is a substance made of weakened or killed disease germs designed to make a body immune to (safe against) that particular infectious disease. Effective vaccines change the immune system (the body's natural defense system against disease and infection) so it acts as if it has already developed a disease. The vaccine prepares the immune system and its antibodies (disease-fighting chemicals) to react quickly and effectively when threatened by disease in the future. The development of vaccines against diseases ranging from polio to smallpox is considered among the great accomplishments of medical science.

Smallpox

The first effective vaccine was developed against smallpox, a fast-spreading disease characterized by high fever and sores on the skin that killed many of its victims and left others permanently disfigured. The disease was so common in ancient China that newborns were not named until they survived the disease. The development of the vaccine (which was injected with a needle) in the late 1700s followed centuries of innovative efforts to fight smallpox.

English physician Edward Jenner (17491823) observed that people who were in contact with cows did not develop smallpox. Instead, they developed cowpox, an illness similar to smallpox but one that was not a threat to human life.

In 1796, Jenner injected a healthy eight-year-old boy with cowpox. The boy became moderately ill, but soon recovered. Jenner then injected the boy twice with the smallpox virus, and the boy did not get sick. Jenner discovered that exposure to the cowpox virus spurred the boy's immune system. The cowpox antigen stimulated the production of antibodies specific to that disease. (An antigen is a substance that stimulates the production of an antibody when introduced into the body.) The antigen conditioned the immune system to move faster and more efficiently against smallpox in the future. Jenner called the procedure vaccination, from the Latin word vaccinus, meaning "of cows." In 1979, world health authorities declared the eradication of smallpox, the only infectious disease to be completely eliminated.

Rabies and poliomyelitis

The next advancement in the study of vaccines came almost 100 years after Jenner's discovery. In 1885, French microbiologist Louis Pasteur (18221895) saved the life of Joseph Meister, a nine-year-old who had been attacked by a rabid dog, by using a series of experimental rabies vaccinations. Rabies attacks the nervous system and can cause odd behavior, paralysis, and death. Pasteur's rabies vaccine, the first human vaccine created in a laboratory, was made from a mild version of the live virus. (Pasteur had weakened the virus by drying it over potash.)

Words to Know

Antibody: A molecule in the immune system that is created to destroy foreign molecules in the body.

Antigen: A substance such as a bacterial cell that stimulates the production of an antibody when introduced into the body.

Epidemic: Rapidly spreading outbreak of a contagious disease.

Immune system: The body's natural defense system that guards against foreign invaders and that includes lymphocytes and antibodies.

Infectious: A type of disease that is spread primarily through contact with someone who already has the disease.

While the viruses that cause poliomyelitis (more commonly known as polio) appear to have been present for centuries, the disease emerged with a vengeance in the early 1900s. Polio wastes away the skeletal muscles and thus brings about paralysis and often permanent disability and deformity. At the peak of the epidemic, in 1952, polio killed 3,000 Americans and 58,000 new cases of polio were reported. In 1955, American microbiologist Jonas Salk (19141995) created a vaccine for polio. When the vaccine was declared safe after massive testing with schoolchildren, the vaccine and its creator were celebrated. The Salk vaccine contained the killed versions of the three types of polio virus that had been identified in the 1940s.

In 1961, an oral polio vaccine developed by Russian-born American virologist Albert Sabin (19061993) was licensed in the United States. The Sabin vaccine, which used weakened, live polio virus, quickly overtook the Salk vaccine in popularity in the United States. Because it is taken by mouth, the Sabin vaccine is more convenient and less expensive to administer than the Salk vaccine. It is currently administered to all healthy children. In the early 1990s, health organizations reported that polio was close to extinction in the Western Hemisphere.

Contemporary vaccines

Effective vaccines have limited many life-threatening infectious diseases. In the United States, children starting kindergarten are required to be immunized against polio, diphtheria, tetanus, measles, and several other

diseases. Other vaccinations are used only by people who are at risk for a disease, who are exposed to a disease, or who are traveling to an area where a disease is common. These include vaccinations for influenza, yellow fever, typhoid, cholera, and hepatitis A.

Internationally, the challenge of vaccinating large numbers of people is immense. Although more than 80 percent of the world's children were immunized by 1990, no new vaccines have been introduced extensively since then. More than 4 million people, mostly children, die needlessly every year from preventable diseases. Worldwide each year, measles kills 1.1 million children, whooping cough kills 350,000, tetanus kills 500,000, and yellow fever kills 30,000. Another 8 million people each year die from diseases for which vaccines are still being developed. While some researchers seek new vaccines, others continue to look for ways to distribute existing vaccines to those in desperate need.

[See also AIDS (acquired immunodeficiency syndrome); Disease; Poliomyelitis ]

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Vaccines

Vaccines

Vaccines are drugs used to increase the body's ability to combat disease organisms. Most vaccines are designed to help the body fight off a specific type of bacterium, protozoan, or virus. Some vaccines have been developed to stop the growth of cancer cells and to protect military troops from biological warfare. The administration of vaccines to animals and humans is called vaccination or immunization. Vaccination is one medical strategy for preventing the spread of infectious diseases. Vaccines encourage the body to build up immunity against disease organisms.

Vaccination

In 1796, an English physician named Edward Jenner developed the first vaccine to protect people from smallpox. Smallpox is caused by a potentially fatal virus that severely blemishes the skin and internal organs. Jenner noticed that cattle handlers infected with a related disease called cowpox did not contract smallpox. Jenner used this observation to test whether exposure to cowpox prevented people from getting smallpox. He introduced the fluids from a cowpox sore into the arm of a young boy. The boy developed cowpox, a mild disease in humans, but did not get smallpox after Jenner exposed the boy to the smallpox virus. (This highly unethical experiment could not be performed today!) The word "vaccine" comes from the Latin vaccus, meaning "cow." Today, smallpox has been effectively eliminated from the human population through vaccination.

Vaccines for vaccination are made from the disease organism. They are composed of either a weakened ("attenuated") form of the live disease organism, the killed disease organism, or chemical components of the disease organism. The cowpox fluids collected by Jenner contained live viruses that he scratched into the boy's body. Vaccination works by stimulating the immune system to produce antibodies against the disease organism. It takes a few days before the vaccine can protect the body, but the antibody -producing cells impart an immunity that can last several years to a lifetime. Booster shots are sometimes given years after immunization with an active vaccine to extend the body's immunity. Many vaccines must be given as several small doses over a six-month or one-year period. This prevents the person from being ill from a large dose given at once. Vaccination is used against a variety of common diseases including diphtheria, polio, rabies, and tetanus. Development of vaccines against HIV (human immunodeficiency virus) and malaria are two of the most active areas of research in twenty-first-century medicine.

Adverse Effects of Vaccines

Many people are concerned that vaccines can have side effects in certain individuals. Several children have fallen ill from the DPT, or diphtheria-pertussis-tentanus, vaccination. Most illnesses from vaccinations are found in individuals who are allergic to the vaccine. Vaccines made from living organisms may cause the same illness physicians are trying to prevent. The oral polio vaccine, containing weakened virus, is designed to remain in the environment after defecation by the person ingesting it. This exposes other people to it, immunizing them. However, a few people exposed this way have contracted polio. The injected form of the vaccine does not carry this risk, but neither does it help immunize other people.


French scientist Louis Pasteur was the first to develop a way to produce effective vaccines. Pasteur's first vaccine was derived from attenuated cultures of the disease organisms. Developed in 1879, it was for fowl cholera found in chickens. The first vaccine he used on humans was for the deadly viral disease rabies.


Passive Immunity

Another form of protection against disease, termed passive immunity, relies on injection of antibodies into the blood. These antibodies perform the same function as a person's own antibodies, attaching to the disease organism and acting as a label that tells immune cells to kill and remove the organism. These antibodies may be collected from laboratory animals immunized against the disease, or may be produced in cell cultures from special cells called monoclonal antibody cells. Passive immunization permits a person to have the protective antibodies already in the body before getting ill from the disease. Passive immunization works immediately after being administered, but gives only temporary immunity; the protective value may disappear after several weeks. Passive immunization is commonly given during influenza or "flu" outbreaks (but is not the same as a "flu shot," which is a true vaccine, given before exposure to the virus). Antivenoms used to treat the bites or stings of venomous insects and snakes are antibodies, and therefore are a form of passive immunization.

see also AIDS; Antibody; Bacterial Diseases; Disease; Immune Response; Immunization; Pasteur, Louis; T Cell; Viral Diseases

Brian R. Shmaefsky

Bibliography

Nester, Eugene W., et al. Microbiology, A Human Perspective, 2nd ed. Dubuque, IA: WCB/McGraw-Hill. 1996.

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vaccine

vaccine (vak-seen) n. a special preparation of antigenic material that can be used to stimulate the development of antibodies and thus confer active immunity against a specific disease or number of diseases. It is usually given by injection but may be introduced into the skin through light scratches; for some diseases (e.g. polio), oral vaccines are available. Many vaccines are produced by culturing bacteria or viruses under conditions that lead to a loss of their virulence but not of their antigenic nature. Other vaccines consist of specially treated toxins (toxoids) or of dead bacteria that are still antigenic. See immunization.

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vaccine

vac·cine / vakˈsēn/ • n. Med. a substance used to stimulate the production of antibodies and provide immunity against one or several diseases, prepared from the causative agent of a disease, its products, or a synthetic substitute, treated to act as an antigen without inducing the disease: there is no vaccine against HIV infection. ∎  Comput. a program designed to detect computer viruses, and inactivate them. ORIGIN: late 18th cent.: from Latin vaccinus, from vacca ‘cow’ (because of the early use of the cowpox virus against smallpox).

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vaccine

vaccine A liquid preparation of treated disease-producing microorganisms or their products used to stimulate an immune response in the body and so confer resistance to the disease (see immunization). Vaccines are administered orally or by injection (inoculation). They take the form of dead viruses or bacteria that can still act as antigens, live but weakened microorganisms (see attenuation), specially treated toxins, or antigenic extracts of the microorganism.

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vaccine

vaccine in v. disease cowpox, v. matter or virus v., v. inoculation vaccination. XVIII. — L. vaccīnus, as used in modL. variolæ vaccinæ cowpox, virus vaccinus virus of cowpox used in vaccination, f. vacca cow; see -INE1.
Also vaccine sb. vaccine matter. XIX. — F. Hence vaccinate (-ATE3) XIX, vaccination XVIII.

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vaccine

vaccine Agent used to give immunity against various diseases without producing symptoms. A vaccine consists of modified disease organisms, such as live, weakened virus, or dead ones that are still able to induce the production of specific antibodies within the blood. See also antibody; immune system; virus

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vaccine

vaccine: see vaccination.

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vaccine

vaccine See inoculation.

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vaccine

vaccine •gamine • bromine • thiamine •dopamine • amphetamine • histamine •quinine • strychnine • mezzanine •spalpeen • Philippine • lycopene •gangrene • terrene • silkscreen •windscreen • citrine • Dexedrine •putting green • Benzedrine •Irene, polystyrene •widescreen • sight screen •chlorine, chorine, Doreen, Maureen, Noreen, taurine •smokescreen • rood screen •sunscreen • fluorine • helleborine •Gadarene • Hippocrene •glycerine (US glycerin), nitroglycerine (US nitroglycerin) •nectarine • wintergreen • Methedrine •evergreen • wolverine • vaccine •glassine • Essene • Rexine • piscine •epicene • glycine • pyroxene •Palaeocene (US Paleocene) •Pliocene • Miocene • Holocene •damascene • kerosene • Plasticine •Pleistocene

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