Why do some people get COVID vaccine side effects?

Why do some people get side effects after COVID-19 vaccines? (AP Illustration/Peter Hamlin)
Why do some people get side effects after COVID-19 vaccines? (AP Illustration/Peter Hamlin)

Scientists say it is a normal reaction.

Posted: Jun 10, 2021 7:19 AM

(ASSOCIATED PRESS) - Why do some people get side effects after COVID-19 vaccines?

Temporary side effects including headache, fatigue and fever are signs the immune system is revving up -- a normal response to vaccines. And they’re common.

“The day after getting these vaccines, I wouldn’t plan anything that was strenuous physical activity,” said Dr. Peter Marks, the U.S. Food and Drug Administration’s vaccine chief, who experienced fatigue after his first dose.

Here's what’s happening: The immune system has two main arms, and the first kicks in as soon as the body detects a foreign intruder. White blood cells swarm to the site, prompting inflammation that’s responsible for chills, soreness, fatigue and other side effects.

This rapid-response step of your immune system tends to wane with age, one reason younger people report side effects more often than older adults. Also, some vaccines simply elicit more reactions than others.

That said, everyone reacts differently. If you didn’t feel anything a day or two after either dose, that doesn’t mean the vaccine isn't working.

Behind the scenes, the shots also set in motion the second part of your immune system, which will provide the real protection from the virus by producing antibodies.

Another nuisance side effect: As the immune system activates, it also sometimes causes temporary swelling in lymph nodes, such as those under the arm. Women are encouraged to schedule routine mammograms ahead of COVID-19 vaccination to avoid a swollen node being mistaken for cancer.

Not all side effects are routine. But after hundreds of millions of vaccine doses administered around the world — and intense safety monitoring — few serious risks have been identified. A tiny percentage of people who got vaccines made by AstraZeneca and Johnson & Johnson reported an unusual type of blood clot. Some countries reserved those shots for older adults but regulatory authorities say the benefits of offering them still outweigh the risks.

People also occasionally have serious allergic reactions. That's why you're asked to stick around for about 15 minutes after getting any type of COVID-19 vaccine — to ensure any reaction can be promptly treated.

Finally, authorities are trying to determine whether temporary heart inflammation that can occur with many types of infections also might be a rare side effect after the mRNA vaccines, the kind made by Pfizer and Moderna. U.S. health officials can't yet tell if there's a link but say they're monitoring a small number of reports, mostly male teens or young adults.

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Cases: 604184

Reported Deaths: 7620
CountyCasesDeaths
Hennepin1248631774
Ramsey52480895
Dakota46804470
Anoka42746458
Washington27416291
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Blue Earth762543
Crow Wing681594
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Benton582998
Goodhue483874
Douglas475381
Mower470733
Winona461251
Itasca459263
Isanti439964
McLeod430361
Morrison424662
Nobles407950
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Steele397616
Polk389072
Becker386655
Lyon363853
Carlton352756
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Nicollet331045
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Brown307840
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Todd285632
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Cases: 370914

Reported Deaths: 6048
CountyCasesDeaths
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Linn21204339
Scott20306247
Black Hawk16119312
Woodbury15238230
Johnson1461585
Dubuque13506211
Dallas1128999
Pottawattamie11223174
Story1071448
Warren583991
Clinton561493
Cerro Gordo553593
Sioux517074
Webster515494
Muscatine4880106
Marshall486676
Des Moines467271
Wapello4337122
Buena Vista426940
Jasper421172
Plymouth402981
Lee382356
Marion366076
Jones300957
Henry294637
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Carroll286852
Crawford268540
Boone268434
Benton259655
Washington256751
Dickinson249344
Mahaska232351
Jackson225242
Clay216627
Kossuth216166
Tama211871
Delaware210943
Winneshiek198535
Page194522
Buchanan193733
Cedar192223
Hardin187444
Fayette186543
Wright185940
Hamilton181851
Harrison179973
Clayton171057
Butler166235
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Mills163724
Floyd163342
Cherokee159338
Lyon158841
Poweshiek157036
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Hancock150234
Iowa149824
Winnebago144531
Cass139255
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Grundy137333
Emmet135841
Jefferson133435
Shelby131537
Sac130920
Union129935
Louisa129749
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Osceola78916
Greene78011
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