Fever, headache, fatigue are all signs the vaccine is working, doctors say

All three of the COVID-19 vaccines available are safe and effective, according to the medical and scientific community. However, they can cause mild to moderate side effects for some people, usually more severe after the second shot. 

There is really no way to tell for sure how your body will react to a COVID-19 shot, but doctors say those symptoms of fatigue, fever, or headache are actually a good thing.

"If you typically don’t have a bad reaction to vaccines, I wouldn’t expect anything different from these vaccines," said University of South Florida virologist, Dr. Michael Teng.

Still, some people experience more side effects after the shot than others.

A few vaccinated individuals told FOX 13 about their symptoms, ranging from "discomfort in the middle of the night" to being "down for a couple of days" to no reaction at all.

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The most common complaint is injection site pain. About 30% of people have symptoms including fatigue, headache, aching muscles and joints, and fever. Doctors say they only stick around about a day or two.

"The second dose is usually a little more severe because the first dose is there to train your immune system and the second dose is there to really rev it up, make a really robust immune response," explained Teng. "So it’s really your immune response that is causing these side effects."

And that’s exactly what it’s supposed to do.

Teng says there are a few factors that determine the severity of after-vaccine reactions.

"The elderly seemed to tolerate the vaccine better, or have fewer side effects, and that the younger people tended to have more side effects," Teng said. "It’s even gender; looks like women may have a little bit greater side effects than men."

Researchers say those symptoms are likely a sign of a more robust immune system. However, a lack of side effects does not mean your immune system is not working properly. How your body reacts to the coronavirus shot is very individualized.

"Of course, I don’t want to be that small percentage that ends up super, super sick," Tari-Lynn Brkljacic told FOX 13 News. "But if it protects me, it protects me, and if it protects my mom and my kids and everyone else, then it’s worth it."

To date, there are no serious, long-term side effects of getting a coronavirus vaccine. Severe allergic reactions are extremely rare and are why recipients are monitored for up to 30 minutes after getting the shot.

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