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

The flu shot can cause mild side effects that are sometimes mistaken for flu. These side effects are caused by a person’s immune system making protective antibodies in response to being vaccinated. These antibodies are what allow the body to fight against flu. It is rare for someone to experience fever, muscle pain, and feelings of discomfort or weakness. If experienced at all, these effects usually last one to two days after vaccination and are much less severe than actual flu illness.

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1. What is seasonal flu?
2. How can I protect myself and others from the flu?
3. Who should get vaccinated this season?
4. Can I get a flu vaccine if I recently had COVID-19?
5. How effective is the flu shot?
6. What are the risks from getting a flu shot?
7. What are the side effects that could occur?
8. Can the flu shot give me the flu?
9. Why do some people not feel well after getting the flu shot?
10. What about people who get a seasonal flu vaccine and still get sick with flu-like symptoms?