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Can I get sick after receiving a seasonal flu shot or H1N1 vaccine?

Marshelya D. Wilson, MD
Family Medicine

Yes, some people can get sick even after receiving the flu vaccine. This is because the vaccine's effectiveness is related to how well it matches the strains found during flu season. Most people who get sick in spite of receiving the flu vaccine will have milder symptoms, though.

The seasonal flu shot and the H1N1 vaccine are one and the same any year that the H1N1 virus is circulating -- and neither shot can make you sick. The flu shot vaccine is made from flu virus that has been killed, which means that it cannot infect your body. Studies comparing the people who got the flu shot to others given a shot of saline solution showed there was no difference in the number of people who experienced flu-like symptoms after the vaccine.

If you come down with the flu right after getting the shot, it's possible that you were exposed to the virus just prior to the shot or in the first two weeks after the shot, before your immunity had fully developed. You may also have caught a flu-like virus or a strain of flu that the vaccine does not protect against. There are many different influenza viruses, and the shot only guards you against the three expected to be most common each flu season.

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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.