Why do some people feel sick after getting the flu shot?

Why should I get my flu shot this year?

This year it is extra important to get your flu vaccine, just to make sure we don’t add more sickness to our already full plate. Most people won’t have any reaction to the flu vaccine, but some people will. Some symptoms include redness or soreness where you got the shot. Less commonly, muscle aches, fever, headache, and nausea.  

Why does the flu shot sometimes make me feel sick?

We don’t know exactly why some people have reactions to the flu vaccine and others don’t. But we do know why it can make you feel a bit sick. The goal of any vaccine is to educate your immune system about a germ without you actually getting infected by the germ. Part of the education requires your immune system to become active. When your immune system is active, it can cause symptoms like a mild fever.

These temporary symptoms can feel similar to having a mild case of the flu, but they aren’t the same as being sick! They are a sign that your body is learning to recognize the real flu virus. In the future, if you come into contact with the flu virus, your body will already know how to fight it. This means you will get less sick, or not get sick at all, if you are exposed to the flu.


Last update: October 16, 2020, 4:06 pm ET

Science review: AGB, GSN, ERS, JAB