If you have questions about whether you should get a flu vaccine, consult your health-care provider

How effective is the flu shot?

With the flu shot, when the "match" between vaccine and circulating strains is close, the vaccine prevents influenza in about 70 percent to 90 percent of healthy persons younger than age 65 years. Among elderly persons living outside chronic-care facilities (such as nursing homes) and those persons with long-term (chronic) medical conditions, the flu shot is 30 percent to 70 percent effective in preventing hospitalization for pneumonia and influenza. Among elderly nursing home residents, the flu shot is most effective in preventing severe illness, secondary complications, and deaths related to the flu. In this population, the shot can be 50 percent to 60 percent effective in preventing hospitalization or pneumonia and 80 percent effective in preventing death from the flu.

What are the risks from getting a flu shot?

The viruses in the flu shot are killed (inactivated), so you cannot get the flu from a flu shot. The risk of a flu shot causing serious harm, or death, is extremely small. However, a vaccine, like any medicine, may rarely cause serious problems, such as severe allergic reactions. Almost all people who get influenza vaccine have no serious problems from it.

What are the side effects that could occur?

• Soreness, redness, or swelling where the shot was given
• Fever (low grade)
• Aches

Can severe problems occur?

• Life-threatening allergic reactions are very rare. Signs of serious allergic reaction can include breathing problems, hoarseness or wheezing, hives, paleness, weakness, a fast heartbeat, or dizziness. If they do occur, it is within a few minutes to a few hours after the shot. These reactions are more likely to occur among persons with a severe allergy to eggs, because the viruses used in the influenza vaccine are grown in hens' eggs. People who have had a severe reaction to eggs or to a flu shot in the past should not get a flu shot before seeing a physician.
• Guillain-Barré syndrome: Normally, about one person per 100,000 people per year will develop Guillain-Barré syndrome (GBS), an illness characterized by fever, nerve damage, and muscle weakness. In 1976, vaccination with the swine flu vaccine was associated with getting GBS. Several studies have been done to evaluate if other flu vaccines since 1976 were associated with GBS. Only one of the studies showed an association. That study suggested that one person out of 1 million vaccinated persons may be at risk of GBS associated with the vaccine association. That study suggested that one person out of 1 million vaccinated persons may be at risk of GBS associated with the vaccine.