Flu Shots (Influenza Vaccine)

What are flu shots?

When you get a flu shot you are injected in the arm with the influenza vaccine. The vaccine helps protect adults and children from getting influenza (flu).

The influenza virus is always present somewhere in the world. In the United States flu outbreaks tend to occur each year between November and March.

Influenza causes a cold like upper respiratory infection. Unlike most colds, however, the flu often causes fever, muscle aches, and dizziness. It can also lead to more serious infections, such as pneumonia. In an average year, influenza is associated with more than 20,000 deaths nationwide and more than 100,000 hospitalizations. These deaths usually occur in the elderly and in people with chronic health problems, such as heart disease and severe asthma.

How do they work?

The formula for the flu vaccine is changed every year according to the recommendations of scientists from the Centers for Disease Control (CDC). They predict which strains of flu virus are most likely to appear the next winter. The flu shot that has been produced this flu season contains three influenza virus strains designated A/Panama, A/New Caledonia and B/Yamanashi.

The virus in the flu vaccine has been inactivated, or "killed." This means you cannot catch the flu from getting a shot. Getting the shot introduces part of the flu virus to your immune system. Your body then reacts by making protective antibodies against the virus.

How effective are they?

When the vaccine viruses and circulating viruses are well matched, the flu vaccine is 70-90 percent effective in preventing influenza among healthy adults. In the elderly and those with certain chronic medical conditions, the vaccine is often less effective in preventing illness. Even if you do get the flu, the vaccine helps protect against severe infection. For this reason it is said that the flu shot protects against death from the flu more than from flu itself.

It takes about 1 to 2 weeks after vaccination for the antibody against influenza to develop and provide protection. Another reason is that antibody resulting from flu vaccine declines over time and antibody levels from one year can be too low to provide protection for the next year.

It is best to get the flu shot in October of each year. Try to get it no later than November, if possible. The Department of Health and Human Services Food and Drug Administration and CDC are working closely with vaccine manufacturers to facilitate the availability of safe and effective influenza vaccine for the upcoming flu season. Influenza vaccine manufacturers have told FDA and CDC to expect delays in flu vaccine shipments and that it is possible there will be reductions of available influenza virus vaccine for the 2000-01 season. For more information please contact CDC.

What are the side effects?

Eggs are used in the production of flu vaccine. If you are allergic to eggs, you may have a severe allergic reaction to the flu shot. The flu shot should not be taken by anyone who has a history of severe egg allergy.

Some manufacturers also recommend not getting a flu shot if you have an allergy to thimerosal. Thimerosal is a preservative used in contact lens solutions and the flu vaccine.

For people who do not have egg or thimerosal allergies, the flu vaccine has infrequent, minor side effects. The most common reaction is some soreness at the site of the shot. A few people develop fever or muscle aches within a few hours of the injection. These symptoms may last 1 to 2 days.

There have been no reports of flu shot complications affecting the nervous system since the 1976-1977 swine flu epidemic.

Who should get a flu shot?

Several groups of people should receive the flu shot every year:

elderly people (65 years and older)
people whose immune systems may be impaired, such as by HIV, cancer, or an organ transplant
people with chronic medical problems, such as asthma, heart disease, emphysema, and diabetes
people working in health care
school teachers and other community workers with close, daily contact with the public.

What precautions should tavelers take against influenza?

The risk for exposure to influenza during travel varies depending on the time of year, destination, and type of travel. In the tropics, such as the Caribbean, influenza can occur throughout the year. In temperate regions of the Southern Hemisphere, such as parts of Australia and South America, most influenza activity occurs from April through September. In countries of the Northern Hemisphere, such as the United States and Canada, influenza generally occurs from November through March. However, in temperate climate zones of the Northern and Southern Hemispheres, travelers can be exposed to influenza during their respective summer months, especially when traveling as part of large, organized tourist groups composed of persons from areas of the world where influenza viruses are circulating.

Exposure to influenza virus during travel can result in clinical illness that begins while traveling. Groups at increased risk for influenza-related complications who should receive influenza vaccination include:

persons aged 50 years or older;
residents of nursing homes and any other chronic-care facilities that house persons of any age who have chronic medical conditions;
adults and children who have chronic disorders of the pulmonary or cardiovascular systems, including children with asthma;
adults and children who have the following medical conditions:

chronic metabolic diseases (including diabetes mellitus),
renal dysfunction,
hemoglobinopathies,
immunosuppression (including immunosuppression cause by medications and by human immunodeficiency virus);

children and teenagers (aged 6 months to 18 years) who are receiving long-term aspirin therapy and therefore might be at risk for developing Reye syndrome after influenza infection;
women who will be in their second or third trimester of pregnancy during the influenza season.

Flu shots can be helpful for anyone who is not severely allergic to eggs.