To avoid getting the flu, or to lessen the severity, you should get a flu shot each fall, especially if you are 50 or older, have a chronic health problem, are a health care worker or live or work around the elderly. A flu vaccination is your best chance to protect yourself. However, while the vaccine has a 67 to 92 percent success rate in healthy adults and children, it may not be 100 percent effective, according to the American Lung Association, because the flu strain it protects against may not be the same as the one that is going around in your area. If you are allergic to eggs, or running a fever, don't get a flu shot without talking first with your health care professional. The flu shot has been shown to be completely safe during pregnancy, but again, discuss this with your health care professional.
Because your immune system takes time to respond to the flu shot, you should get vaccinated in early fall -- six to eight weeks before flu season begins. Flu season begins around October in the Northern hemisphere and April in the Southern hemisphere.
However, if you can't get vaccinated then, it is still worth getting vaccinated any time right up to the beginning of the flu season. You start to develop some immunity from the shot within a few days to two weeks.
The vaccine itself cannot cause flu, but you could become exposed and infected soon after vaccination, before antibodies develop, then come down with the flu and attribute it to the shot. You may also become exposed to viruses other than the influenza virus, which have similar symptoms, and think you have the flu. The vaccine can cause side effects, especially in children who previously have not been exposed to the flu virus. The most common side effect is soreness at the site of the vaccination. Others include fever, tiredness and sore muscles that may begin six to 12 hours after vaccination and may last for up to two days. These symptoms are not influenza itself but an immune response to the virus proteins in the vaccine.