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Can the Flu Shot Cause the Flu?

A flu vaccine cannot give the flu to someone. Viruses in the vaccine have been Akilled,@ making them unable to cause influenza. Common, mild side effects can occur from a flu shot, including soreness, redness or swelling where the shot was given. Some fever or aching may also occur after a shot, but this is not the flu. Serious reactions to the vaccine are rare and occur within minutes to a few hours after the shot. This may be because a person’s system is very sensitive to a vaccine ingredient.

It takes up to two weeks to develop protection against the flu after receiving the shot. It is possible to be exposed to the flu during that time and become ill before the vaccine takes effect. Also, the vaccine is not effective against all strains of flu virus. It only protects against the viruses for which it has been prepared each year. So a person can become ill from a flu virus not included in the vaccine. If a cold or respiratory illness occurs soon after a flu shot it is often coincidental and unrelated to the vaccine.

The elderly do not respond to the vaccine as well as someone who is younger and healthier, so the degree of protection is not as great with the vaccine. In some cases older people can become ill with the flu, but it will be a milder case. A flu shot for the elderly is most effective to prevent severe flu illness, which can lead to pneumonia and even death.

To prevent illness while traveling abroad, one should receive any recommended or required vaccinations before entering another country. This should occur at least 4-6 weeks before travel to allow time for vaccines to take effect. Consult a doctor who specializes in travel health and knows what diseases are prevalent in the area in which you plan to travel. The Centers of Disease Control and Prevention recommends that all travelers should take the following precautions: