You're Most Likely to Have This One Vaccine Side Effect, Study Says

Researchers in the U.K. found that this side effect is the most common after both shots.

The rollout of COVID vaccines is finally beginning to pick up the pace across the U.S. as early kinks in the system are worked out and as states begin to open access to new demographics. As they're administered to larger groups of people, it's becoming more and more apparent which side effects you can expect when it's your turn to sit down for a shot. Now, a newly published study out of the U.K. has found that one side effect is the most common of all. Read on to see what you're most likely to experience after your jab, and for more on the top infectious disease expert's experience, check out Dr. Fauci Says He Had These Side Effects From His Second Vaccine Dose.

Nearly half of patients experience swelling and pain at the injection site.

Woman with pain in upper arm

A recent study conducted by the U.K.'s National Health Service (NHS) analyzed feedback from 40,000 patients—the majority of whom were healthcare workers—who had received at least one dose of the Pfizer-BioNTech vaccine through early January, the BBC reports. These patients tracked their side effects through the self-reported app Zoe COVID Symptom Study. Results showed that 37 percent of respondents reported minor local "after-effects" including swelling and pain at the injection site after the first dose and 45 percent of patients felt the side effect after the second. And for the side effects of the newest vaccine, check out These Are the Side Effects of the New Johnson & Johnson Vaccine.

Chills, a fever, and aches are less common.

Young man suffering with fever and chills while sitting wrapped in a blanket on the sofa at home

While local side effects—those mainly relegated to the injection site—are quite common, systemic side effects—which have a broader affect on the body—were slightly less so. Just 14 percent of those observed in the U.K. study said they experienced chills, fever, or aches after their first dose and 22 percent reported them after their second dose.

Researchers noted that all side effects resolved themselves within a few days and are signs your body is responding to the vaccine. "Generally, most people should be reassured by this data," Tim Spector, PhD, lead Zoe app researcher and professor of genetic epidemiology at King's College London, told the BBC. And for more on signs of a successful shot, find out why Dr. Fauci Says These 2 Side Effects Mean Your COVID Vaccine Is Working.

The Moderna clinical trials had similar findings.

Photo of mature man suffering from pain in arm
ljubaphoto / iStock

The most common COVID vaccine side effect that Moderna patients reported, according to data from their clinical trials, was also pain at the injection site. In that case, a whopping 92 percent of those vaccinated experienced this side effect. And for more regular COVID news, sign up for our daily newsletter.

People who had COVID are almost twice as likely to experience at least one whole body side effect.

Woman touching forehead, having headache in the morning, sitting on bed
Prostock-Studio / iStock

Thirty-three percent of those studied who had previously had COVID-19 reported at least one whole body side effect within the seven days after getting vaccinated. That's nearly twice as many as the 19 percent of people who had not previously had COVID who had a systemic reaction.

"It's interesting to see that those with previous COVID are more likely to experience these mild after effects than naive subjects," Spector said in a statement. "This could be good news, as a larger response like this suggests that those getting a first dose after having had COVID are generating a stronger immune reaction and may get greater protection from just a single shot of the vaccine." And for more on where you can get your vaccine, check out If You Live in These States, You Can Get Vaccinated at Walgreens Next Week.

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Zachary Mack
Zach is a freelance writer specializing in beer, wine, food, spirits, and travel. He is based in Manhattan. Read more
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