Side effects of the inactivated influenza vaccine

Because the vaccine contains killed virus, the influenza shot cannot cause the flu. If you develop the flu after being immunized, it may be because you were exposed to the flu virus before receiving the injection or you were exposed to another virus that the vaccine did not protect against.

Some minor side effects of the immunization have been reported and may include:

• Discomfort at the site of the shot. This is the most frequent side effect in adults and may last 1 to 2 days.
• Fever, vague feelings of weakness, and muscle aches. These may occur 6 to 12 hours after the flu shot and last 1 to 2 days.

Acetaminophen or ibuprofen can help relieve any minor side effects. Do not give aspirin to anyone younger than 20 because of the risk for developing Reye's syndrome.

No reports have been confirmed of Guillain-Barré syndrome developing in people as a result of the influenza vaccine since the 1976 vaccination program. During that year, the swine flu vaccine was associated with an increase in the syndrome. Guillain-Barré syndrome is the only known possible fatal reaction to influenza vaccine and is extremely rare. The risk of death from the flu vaccine is estimated at 1 person in 2 million and is significantly lower than the risk of dying from complications caused by the flu.