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Why do some people not feel well after getting the flu shot?

The most common side effect of the flu vaccine in adults is soreness at the spot where the shot was given, which usually lasts less than two days. The soreness is often caused by a person’s immune system making protective antibodies to the killed viruses in the vaccine. These antibodies are what allow the body to fight against flu. The needle stick may also cause some soreness at the injection site.

According to the Advisory Committee on Immunization Practices (ACIP), rare symptoms include fever, muscle pain and feelings of discomfort or weakness. If these problems occur, they are very uncommon and usually begin soon after the shot and last 1 to 2 days.

Some people do not feel well after getting the flu shot due to a different virus, not because of the flu shot. Many people report that they get the flu after getting a flu shot. There is no active virus in a flu shot so people can not get sick from the vaccine. The flu shot is given during cold and flu season and it can take two weeks for the body to make antibodies against the flu. So if a person gets sick after the flu shot it is due to a different virus and not the vaccine.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.