This Vaccine Side Effect Could Mean You Already Had COVID, New Study Says

Research has found that this reaction is much more common in those previously infected.

Anyone who gets the COVID vaccine can experience a multitude of side effects, according to the Centers for Disease Control and Prevention (CDC). From arm swelling to fever, these reactions are just how some people's bodies respond to building immunity against COVID. But as it turns out, your specific vaccine reactions may also offer insight into your previous experience with the virus. According to new research, one vaccine side effect in particular may indicate that you have already had COVID. Read on to find out which reaction to look out for, and for more on surprising side effects, discover The Common Vaccine Side Effect That No One Is Talking About, Experts Say.

People who already had COVID are more likely to experience swollen lymph nodes after vaccination.

Woman suffering from sore throat.

A new study has found that certain vaccine side effects are more common in people who have already had COVID. The study, which was made available April 22 as a preprint on medRxiv, analyzed 947 people who were monitored after their vaccination for side effects—265 of whom had previously been infected with COVID. The researchers found that one unusual side effect—swollen lymph nodes or lymphadenopathy—was much more common in those who had previously had COVID. According to the study, less than 1 percent of people with no history of COVID reported experiencing lymphadenopathy after vaccination, while 4 percent of those who had been infected with the virus experienced this side effect. And for more on vaccine reactions, Doing This After Your Vaccine Can Make Side Effects Worse, Doctors Say.

Other side effects are more common in people with prior COVID infection as well.

Shot of a young man checking his temperature while lying on the couch at home

There were four more side effects also more common in those who had been previously infected with the coronavirus: fever, fatigue, myalgia (muscle pain), and arthralgia (joint pain). According to the study, fever was experienced by 8 percent of those who had COVID, but only 2 percent of those who had not been infected reported it. Fatigue was reported by 29 percent of those who had COVID, and 20 percent who hadn't. Myalgia was reported by 30 percent of those who had COVID and only 15 percent who had not, while arthralgia was a side effect for 17 percent of people with a COVID history and only 7 percent of those who had never been infected. And for more on life after vaccination, The CDC Says People Who Get COVID After Vaccination Have This in Common.

People with prior COVID infection are more likely to have vaccine side effects in general.

Sick young woman lying on the couch and holding her head with hand. Ill woman lying on the sofa with high temperature.

According to the study, people who had previous coronavirus infections were more likely to report side effects in general after getting the COVID vaccine. People who had COVID were also more likely to report at least one moderate to severe vaccine side effect. However, vaccine reactions occurring local to the vaccine injection site—like arm redness and swelling—and gastrointestinal symptoms were not more prevalent in those with prior COVID infection than those without. And for more up-to-date information, sign up for our daily newsletter.

Some experts think that people who have already had COVID only need one vaccine dose.

female doctor giving COVID-19 vaccine of a mid adult women with protective face mask in the doctor's office

Many experts question whether people who have had COVID actually need the second dose, as more reactions to the vaccine may mean more antibodies are formed after only one dose for those who have had prior infections. In fact, the researchers for this study conclude that their data "adds weight to the question of whether a second dose of mRNA vaccine is necessary in those with previous COVID-19, assuming effective immunity is established after the first dose."

However, the CDC still says that you should get two shots of the Pfizer or Moderna vaccines, whether or not you've had COVID already. And aside from extremely rare allergic reactions, normal vaccine side effects should not dissuade you from your second dose either. "You should get your second shot even if you have side effects after the first shot, unless a vaccination provider or your doctor tells you not to get it," the CDC says. And for more vaccine guidance, Don't Do This for 2 Days After Your COVID Vaccine, Doctors Say.

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