The flu vaccine protects a person against getting influenza , caused by the influenza virus. It is administered either by injection or by inhalation.
There are two types of flu vaccine. Live attenuated influenza vaccine (LAIV) was first approved for use in 2003. It contains live, but weakened, influenza virus and is administered as a nasal spray. Inactivated influenza vaccine contains killed viruses and is given by intramuscular injection.
Because influenza changes from year to year, a flu shot, unlike other types of vaccinations, is required every year. Each year, the United States Centers for Communicable Disease Control predicts the strains of influenza that are likely to appear in the coming year. Vaccine manufacturers then make products to protect against these types of flu. These vaccines only protect against the type of influenza viruses from which they are made. They are usually of no value against other types of influenza virus.
There are three types of influenza virus: A, B, and C. They differ by the proteins on their outer surface. Type A viruses are found in many different animals, including ducks, chickens, pigs, whales, horses, and seals. Influenza B viruses circulate widely, but only among humans. Type C viruses, also only among humans, cause a very mild infection, and flu vaccines do not include protection against type C influenza.
Influenza is a contagious illness. Every year, 10 to 20 percent of the U.S. population gets the flu, and over 100,000 people are hospitalized because of influenza. Symptoms of flu include fever , headache , extreme tiredness, dry cough , sore throat , runny or stuffy nose, and muscle aches. When children get the flu, they often complain of nausea and have vomiting and diarrhea , although these problems are less common in older children and adults. While influenza virus vaccines cannot give complete protection against flu, they greatly reduce the risk of flu-like infections, reduce the risk of hospitalization , and shorten the duration of these infections.
All healthy children between the ages of six months and 23 months should receive influenza vaccine because these young children do not yet have fully developed immune systems and are at increased risk of getting the flu and requiring hospital treatment. Children over the age of six months should also receive the vaccine if they have certain medical risk factors:
- asthma or other lung disease
- congenital heart disease with defects that require medications or surgery or other heart disease
- glomerulonephritis, kidney failure, or other kidney disease
- diabetes or other metabolic disease
- sickle cell disease or other anemia
- immune system problems or other anemia
- juvenile rheumatoid arthritis or any other disease needing aspirin therapy
Otherwise healthy children above the age of 23 months may have a flu shot simply to reduce the risk of influenza.
Most people have no adverse effects from a flu shot other than soreness at the injection site that lasts a few days. The greatest risk is an allergic reaction, which can be serious, but this is very rare. A low fever occasionally occurs.
Vaccines should not be given to patients taking antibiotic drugs. While both flu vaccines may be administered at the same time as other vaccines, if two vaccines are not given at exactly the same time, they should be spaced four weeks apart.
Flu vaccine should not be given to the following groups:
- children with a severe allergic reaction to chickens or egg protein
- children who have exhibited a moderate to severe reaction after a previous influenza shot
- children who have ever been paralyzed due to Guillain-Barré syndrome
- children who are sick with anything beyond a slight cold
Unlike the swine flu vaccine used in 1976, flu vaccines in the last decades of the twentieth century and early 2000s have shown no association with Guillain-Barré syndrome (GBS) in children.
Both types of influenza vaccine may be administered to family members of immunosuppressed patients, as long as the patients do not require a protected environment, although the killed virus vaccine is preferred for this purpose. Family members of patients who do require a protected environment, such as people who have had a stem cell transplant, should only receive the killed virus vaccine (injection).
Parents, siblings, and other people who will be in close contact with a sick child or adult should have a flu shot whether or not they need it for their own protection.
The risk of a local reaction to a flu injection increases with age. Children under the age of 13 years rarely have reactions to the flu vaccine. Over the age of 13 years, about 10 percent of children have a reaction to the shot.
Since flu season is usually in late fall or early winter, a flu shot should be given in the autumn, so that full immunity can be built up. However, it is never too late to get a flu shot.
Attenuated —A live but weakened microorganism that can no longer produce disease.
Guillain-Barré syndrome —Progressive and usually reversible paralysis or weakness of multiple muscles usually starting in the lower extremities and often ascending to the muscles involved in respiration. The syndrome is due to inflammation and loss of the myelin covering of the nerve fibers, often associated with an acute infection. Also called acute idiopathic polyneuritis.
Influenza —An infectious disease caused by a virus that affects the respiratory system, causing fever, congestion, muscle aches, and headaches.
Vaccine —A substance prepared from a weakened or killed microorganism which, when injected, helps the body to form antibodies that will prevent infection by the natural microorganism.
See also Influenza; Vaccination.
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Samuel Uretsky, PharmD