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These 5 Things Make You More Likely to Have COVID Vaccine Side Effects

These factors increase your chances of a post-shot reaction.

Some people who've gotten the COVID vaccine have reported mild and temporary side effects, including fatigue, injection-site pain and fever. It's not an experience anyone looks forward to, but experts say such reactions are a positive sign. They indicate that the vaccine is working, training the immune system to fend off the coronavirus before it causes serious illness or death. According to what scientists know from the hundreds of millions of vaccines given so far, some factors make you more likely to experience those side effects. Here are five things that raise that risk. And to get through this pandemic without catching coronavirus, don't miss this essential list: Things You Should Never Do Before Your Vaccine.


Being Female

Woman in medical face mask getting Covid-19 vaccine at the hospital

According to a CDC study which analyzed the first month of vaccinations, more than 79% of side effects were reported by women, although only 60% of vaccines were given to women. Why? Women may be more likely to report side effects, or the female body may produce a more aggressive immune response against the coronavirus (which would also explain why more men seem to die of COVID-19). 

Dr. Allison Arwady, the Chicago Department of Public Health Commissioner, told NBC 5 Chicago that estrogen can elevate immune responses, while testosterone can decrease it. Many immune-modulating genes live on the X chromosome; women have two while men have one. "So there's all these reasons that sort of immunity in general goes up a little bit different in women than it does in men," she said. "And so we're seeing women a little more likely to report some of the side effects."


Being Young

Happy vaccinated woman gesturing thumbs up.

In clinical trials of the COVID vaccines, young people reported more side effects than older people. Younger people have more robust immune systems that can produce stronger responses to invaders. That might prompt a vaccine to cause more noticeable side effects.


Previous COVID Infection

Woman suffering from cold, virus lying on the sofa under the blanket

Clinical trials found that people who'd already had COVID-19 had more vaccine side effects than people who had not been infected. That could be because the immune system remembers the virus from the previous infection and mounts a strong response to the vaccine. 


Getting the Second Dose of the Vaccine

A woman displays her vaccination card and the

In people whose bodies haven't experienced the coronavirus, an immune response takes time to build. That could be why some people who haven't had COVID-19 have reported more side effects after receiving their second dose of the Pfizer and Moderna vaccines—the first shot introduced the body to the spike proteins of the coronavirus, and the second shot causes a "recall" response, which causes short-lived side effects like fatigue, muscle aches, fever and chills.


Getting the Moderna Vaccine Vs. Pfizer


According to a study published last week in JAMA, people who got the Moderna vaccine say they experienced more side effects than people who get the shots developed by Pfizer/BioNTech. Of the Moderna recipients, 73 percent reported an injection-site reaction, compared with 65 percent of people who got a Pfizer shot. Nearly 51 percent of those who got the Moderna vaccine had full-body side effects, compared to 48 percent of Pfizer recipients. Experts aren't sure why, but the data hasn't shown that the Moderna vaccine is less safe.

RELATED: This COVID Vaccine Has the Most Side Effects, Study Says


How to Survive This Pandemic

couple of happy people in love smiling and looking at the camera wearing medical and surgical mask on the face to prevent covid-19 or any type of disease or flu

As for yourself, do everything you can to prevent getting—and spreading—COVID-19 in the first place: Wear a face mask, get tested if you think you have coronavirus, avoid crowds (and bars, and house parties), practice social distancing, only run essential errands, wash your hands regularly, disinfect frequently touched surfaces, and to get through this pandemic at your healthiest, don't miss these 35 Places You're Most Likely to Catch COVID.

Michael Martin
Michael Martin is a New York City-based writer and editor whose health and lifestyle content has also been published on Beachbody and Openfit. A contributing writer for Eat This, Not That!, he has also been published in New York, Architectural Digest, Interview, and many others. Read more about Michael