Chickenpox (Varicella)

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Chickenpox (Varicella)


Disease History, Characteristics, and Transmission

Scope and Distribution

Treatment and Prevention

Impacts and Issues

Primary Source Connection



Chickenpox is a viral disease primarily of children, although it can infect any non-immune person. Infection is caused by the varicella-zoster virus (VZV), which is stored in human hosts and is transmitted via direct contact, as well as by inhalation of contaminated airborne particles. Infection with this virus results in the formation of an itchy rash that is sometimes accompanied by a fever. Treatment usually centers on the symptoms of the infections—the rash and fever—rather than on the virus itself. However, antiviral medication may be administered in severe cases. Complications such as bacterial infections, brain infections, viral pneumonia, and even death occur rarely. Following recovery from chickenpox, the virus remains in the body and can be reactivated, causing a new disease called shingles.

Chickenpox is a worldwide disease and most people will develop it by adulthood. Immunity develops after the infection. However, there is a vaccine available that is 80– 90% effective. If a vaccinated person develops chickenpox, the vaccination appears to lessen the severity of infection.

Children develop chickenpox most frequently, although adults tend to have more severe infections. High-risk groups include those with compromised immune systems, newborns, and pregnant women. Individuals in these groups are also unable to use the vaccine due to the risk of developing the disease from the vaccine.

Disease History, Characteristics, and Transmission

Chickenpox has existed for centuries. Originally, doctors were aware of the disease without knowing its cause. Similarities between chickenpox and smallpox, a deadly disease that no longer occurs in humans, made it hard for practitioners to differentiate between the two. The first description of chickenpox on record was made by the Italian scientist Giovanni Filippo during the 1500s. Subsequently, English physician Richard Morton identified the disease in the 1600s, as did the English physician William Heberden in the 1700s. Heberden first demonstrated that chickenpox and smallpox are different diseases.

Chickenpox is a viral disease that arises when humans become infected with the varicella-zoster virus (VZV), which is a type of human herpes virus. Humans are a reservoir for VZV and the virus is very contagious among humans. Transmission occurs when airborne particles from infected people are inhaled, or when direct contact occurs between infected and non-infected people. Therefore, coughing and sneezing spreads the virus, as does touching the open lesions of infected persons. There is a 70–80% chance that a person who has no history of chickenpox will get the disease following exposure to an infected person.

VZV has an incubation period of about 14–16 days after which the first symptoms appear. Chickenpox is characterized by the formation of itchy blisters that break out most commonly on the scalp, face, and torso. These blisters form vesicles that contain an infectious fluid, and within a day of developing, the blisters break and crust over. Blisters tend to continually form over a period of five to 10 days and the outbreak is over when all sores have formed a crust. Scratching the blisters may cause scarring. Accompanying symptoms include mild fever and weakness.

A person is contagious approximately one to two days prior to the rash developing, and he or she remains contagious until all the blisters have crusted over. Since the incubation period is two to three weeks, a person may be unaware they have contracted the disease until weeks after contact with an infected person.

While most cases of chickenpox are not considered serious, and recovery is likely, the disease potentially can be fatal in both children and adults. Complications can arise, such as bacterial infections under the skin, within bones and tissue, in the lungs, and in the blood. The virus can also cause complications directly, such as encephalitis and viral pneumonia. Prior to the development of a vaccine, approximately 100 people died from chickenpox in the United States every year.

Following recovery from chickenpox, the varicella virus remains in the body and settles among nerve fibers. The virus tends to remain dormant, but it can be reactivated and result in a different infection known as shingles or zoster. This infection generally occurs in older people and is characterized by a painful rash, fever, headache, body aches, and general feelings of illness. While recovery is likely from shingles, many patients suffer ongoing complications, in particular, post-herpetic neuralgia. Post-herpetic neuralgia is nerve pain that arises most likely as a result of the virus becoming active within the nerve fibers and damaging them. This pain can vary from mild to severe and may be present for only three months, or for life. In general, people do not suffer a second case of chickenpox, but there have been some exceptions.


IMMUNOCOMPROMISED: A reduction of the ability of the immune system to recognize and respond to the presence of foreign material.

POSTHERPETIC NEURALGIA: Neuralgia is pain arising in a nerve that is not the result of any injury. Postherpetic neuralgia is neuralgia experienced after infection with a herpesvirus, namely Herpes simplex or Herpes zoster.

VACCINE: A substance that is introduced to stimulate antibody production and thus provide immunity to a particular disease.

VARICELLA ZOSTER IMMUNE GLOBULIN (VZIG): Varicella zoster immune globulin is a preparation that can give people temporary protection against chickenpox after exposure to the varicella virus. It is used for children and adults who are at risk of complications of the disease or who are susceptible to infection because they have weakened immunity.

VESICLE: A membrane-bound sphere that contains a variety of substances in cells.

Scope and Distribution

Chickenpox is a worldwide virus. Its prevalence within society is so high that by adulthood almost all people will have contracted the disease. While children contract the highest number of cases, anyone who comes in contact with an infected person, and has not previously had the disease, is at risk of becoming infected with the virus. In the United States, approximately 4 million cases of chickenpox are reported annually, and despite vaccinations, fatalities still occur.

When children of school age contract the virus, they are required to stay home from school until they are no longer contagious. However, due to the high infectiousness of this disease, outbreaks are hard to prevent, and despite policies that keep infected children at home, outbreaks are likely to occur.

Adults also contract the virus, although the number of adult cases is much lower than the number of cases among children. Despite this, prior to the release of a vaccine in the United States, half of all fatalities were adults. This statistic highlights the fact that adults tend to develop more severe cases of chickenpox.

There are also groups of high risk people within society. These include immunocompromised people, pregnant women, newborn babies, and healthcare workers. Immunocompromised people include cancer and AIDS patients, as well as transplant recipients. Their immune systems are less able to fight off infection, making them more likely to contract the virus. Chickenpox infection during pregnancy may result in complications with the fetal development. These complications may include growth retardation, such as underdevelopment of limbs and lack of growth in some parts of the brain. In addition, a chickenpox infection during pregnancy may lead to miscarriage, premature labor, or infection of the fetus with the virus. Newborn babies have an increased fatality rate if they contract the disease and do not receive treatment. Healthcare workers and people taking care of sick family members are also at risk of contracting the virus.

The development of a second bout of chickenpox is rare and does not seem to be predetermined by any condition. However, the occurrence of shingles tends to be more likely in people 50 years old or older and in immunocompromised people. Shingles is not as common as chickenpox, but still has an annual rate of 1 million cases annually in the United States. Of these, approximately 20% will develop post-herpetic neuralgia. However, shingles does not spread from person to person, but arises in people who already have the varicella-zoster virus in their bodies. And, although shingles can cause chickenpox in non-infected people, it is not as contagious as chickenpox and usually requires contact with the blister fluid in order for transmission to occur. As of May 2006, a vaccine against shingles was approved and is recommended by the CDC for all adults over the age of 60.

Treatment and Prevention

Most cases of chickenpox do not require treatment for recovery to occur. In general, treatment is provided for the symptoms, namely the fever and rash. Fever is treated with non-aspirin medications, such as acetaminophen, since aspirin is linked with the development of Reye's syndrome. The rash is generally treated with calamine lotion, cool compresses, or oatmeal baths to alleviate the itching.

However, in some cases, more specific treatment is employed. Antiviral medication may be given to adults or to children at risk of developing a serious illness. In addition, bacterial infections may arise when blisters are scratched and opened, and anti-bacterial medication may be necessary. Bacterial infections can be prevented by avoiding scratching the blisters, and keeping them clean.

After infection with the chickenpox virus, most patients have a lifelong immunity to the disease. This reduces their chances of contracting the virus again, but it does not keep them from developing shingles. Newborn babies receive immunity from immune mothers, but this immunity lasts only for the first few months of their lives.

A vaccine is available to prevent chickenpox. The vaccine was developed in Japan and the United States and was first released in the United States in 1995. Vaccination is recommended for children between the ages of 12 and 18 months, since this ensures the best protection, but the vaccine can also be given to people older than 18 months. In children under 13 years old, one dose of the vaccine is necessary, whereas those 13 years old and older require two doses administered four to eight weeks apart. Some people do develop chickenpox after being vaccinated, but they tend to have very mild cases of the disease. Vaccination is recommended for almost everyone who has not had chickenpox with the exceptions noted below.

Some individuals should not be vaccinated against chickenpox, including newborns, children with leukemia or lymphoma, people with immune problems, people taking drugs that suppress the immune system, and pregnant women, because of the risk that they may develop the disease as a result of the vaccination. However, if a person in one of these categories is exposed to the virus, they can receive a temporary protective vaccine known as varicella zoster immune globulin (VZIG). VZIG acts to prevent the development of the disease or to modify the disease after exposure. The protection conferred by VZIG is only short term and the treatment is expensive. As a result, it is only administered to people at high risk of developing severe chickenpox when they are exposed to the virus.

During an outbreak of chickenpox, disease transmission can be minimized by separating those with the disease from others and by limiting the duration of any contact that must occur between infected and noninfected individuals. Since chickenpox is highly contagious, anyone who is not immune to the disease should avoid inhaling contaminated air and touching open lesions on infected people. Protection from shingles patients is less difficult due to the fact that transmission occurs via contact with rash fluid only. If these rashes are well covered, risk of transmission is greatly reduced.


Questions sometimes arise as to whether varicella vaccine should be administered to a healthy child who has intimate personal contact with an immunocompromised individual (e.g., a sibling with leukemia, or an immunocompromised individual in their household). With regard to this issue, the Centers for Disease Control and Prevention, National Immunization Program states that the, “ACIP (Advisory Committee on Immunization Practices) and the American Association of Pediatrics (AAP) recommend that healthy household contacts of immunocompromised persons be vaccinated. This is the most effective way to protect the immunocompromised person from varicella. However, because of the small risk of household transmission of vaccine virus, vaccinees who develop a vaccine-related rash should avoid contact with immunocompromised persons while the rash is present. If a susceptible immunocompromised person is inadvertently exposed to a person with a vaccine-related rash, varicella zoster immune globulin (VZIG) need not be given because disease associated with this type of transmission would be expected to be mild. It is preferable to expose the immunocompromised person to the much lower risk of severe disease due to vaccine virus than to wild virus in household contacts.”

SOURCE: Centers for Disease Control and Prevention, National Immunization Program

Impacts and Issues

Despite the availability of an effective vaccine, many people are still not vaccinated against chickenpox for a number of reasons. The benefits associated with vaccination must be weighed against such factors as the cost, importance, and likely impact the vaccination will have. In developing countries, there are many diseases with high rates of morbidity and mortality that can be prevented by vaccination. Vaccination against chickenpox may not be as high a priority as vaccinations against other diseases, especially when funding is limited and the health care delivery system is overburdened.

In countries where the vaccine is affordable, generally available, and of significant benefit to the public health, many still avoid getting vaccinated. People may remain unvaccinated voluntarily because of misconceptions surrounding the seriousness of this disease. Many people are under the impression that chickenpox is a relatively mild virus that all people will encounter and recover from during their lives. However, complications and deaths occur from chickenpox infections, even in healthy individuals. Prior to the vaccine being made available in the United States, 100 people died annually from this disease. These people were not all high-risk patients, but rather, most were healthy individuals. Since vaccination was introduced, the Centers for Disease Control and Prevention (CDC) was still reporting deaths during 1999 and 2000 among healthy, unvaccinated people.

Vaccination appears to be a more cost-effective option for many populations, since the costs of preventing cases of chickenpox often outweigh the costs of combating an outbreak and treating those who contract the disease.

Primary Source Connection

In this newspaper article appeared in the Washington Times during the 2003 school year. The author, Denise Barnes, describes the actions that were taken after hundreds of students in Washington, D.C., failed to provide proof of their immunization status to school officials. Vaccination for chickenpox is required by the school district when students cannot verify that they have had the disease.

Time's Up on School Shots; 434 Students Sent to Court

D.C. public school officials yesterday referred 434 students to truancy court after they failed to provide updated immunization records after 30 days of school. Officials reminded their parents that they could face fines and jail time.

“We're going to court,” said Ralph Neal, assistant schools superintendent. “It's been a whole month.”

Mr. Neal said the D.C. Compulsory School Attendance Amendment Act of 1990 states that principals must refer students to truancy court if they fail to provide proof of immunizations by Oct. 1. He also said Superintendent Clifford B. Janey told principals yesterday to begin the legal process.

“Parents, if convicted, could be fined $100 or [spend] up to 10 days in jail,” Mr. Neal said.

The biggest problems remain in middle, junior and high schools, which have 379 of the students. Among them, 285 are in senior high schools and 94 are in junior highs or middle schools.

The remaining 55 students are in elementary schools and special education centers. The District has 60,799 students in about 200 schools, including specialty schools and programs.

Officials estimated in mid-August that about 5,000 students were still without the mandatory shots and said they would know more when school started Sept. 1. They reported in mid-September that the number had been reduced to 1,190 students.

The school system in August 2003 had about 11,000 students without shots, which means the number of noncompliant students was reduced by more than 50 percent this summer, said Dr. Karyn Berry of the city's Department of Health.

The students who did not receive their shots or provide up-to-date proof were allowed inside schools but were kept in designated areas such as auditoriums or classrooms.

The required shots are DPT (for diphtheria, pertussis and tetanus), OPV (oral polio vaccine), MMR (measles, mumps and rubella), HIB (haemophilus influenza type B), HepB (hepatitis B), and varicella immunizations, if students have not had chicken pox.

“We've worked collaboratively with parents, and we are pleased that more than 60,000 parents have worked along with us,” Mr. Neal said. “But we have [about] 400 students [without shots.] And the law states they must be immunized. Students not attending school are truant. Being a truant means that you are in violation of the law. We need to hold everyone accountable, and we need the cooperation of parents.”

The District has improved the situation, in part, by offering free shots at clinics.

Vera Jackson, a spokeswoman for the city's Department of Health, said six clinics remain open, and no appointment is necessary.

“We're still working very hard to make sure everybody gets immunized,” she said.

Denise Barnes


See AlsoAIDS (Acquired Immunodeficiency Syndrome); Cancer and Infectious Disease; Childhood Infectious Diseases, Immunization Impacts; HIV; Meningitis, Viral; Shingles (Herpes Zoster) Infection; Smallpox; Vaccines and Vaccine Development; Viral Disease.



Mandell, G. L., J. E. Bennett, and R. Dolin. Principles and Practice of Infectious Diseases. 6th ed. Philadelphia, PA: Elsevier, 2004.

Web Sites

Centers for Disease Control. “Varicella Disease (Chickenpox).” May 26, 2005. <> (accessed March 8, 2007).

Centers for Disease Control. “Varicella Vaccine (Chickenpox).” April 25, 2005. <> (accessed March 8, 2007).

U.S. Department of Health and Human Services. “FDA Licenses Chickenpox Vaccine.” March 17, 2005. <> (accessed March 8, 2007).

World Health Organization. “Immunization, Vaccines, and Biologicals: Varicella Vaccine.” May 2003. <> (accessed March 8, 2007).