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Most People Had This COVID Vaccine Side Effect

You might experience this after your first or second shot.
FACT CHECKED BY Emilia Paluszek

After you receive the COVID-19 vaccines by Pfizer or Moderna, you might experience some minor, brief side effects similar to the flu: Fever, chills, body aches. Here's why: "Both Pfizer and Moderna are considered 'reactogenic' in that they stimulate a strong immune response with unpleasant but temporary side effects," explains Dr. George Hwang, an anesthesiologist in Arlington, Virginia, who recently experienced side effects himself after receiving the vaccine—what he calls "the happiest headache, fever and chills I ever had." That's because he knew they were a sign his body had begun developing immunity to COVID-19. Here are the seven most frequently reported post-shot side effects for the Pfizer and Moderna vaccines, from least common to most common. Read on, and to ensure your health and the health of others, don't miss these Sure Signs You've Already Had Coronavirus.


You May Have a Fever

Sick woman with fever checking her temperature with a thermometer at home

After the vaccine is injected into your arm, your cells take in mRNA that encodes a version of the coronavirus's spike protein. And the body reacts. "The innate immune system sets off alarms to recruit more immune cells to your arm, causing inflammation and soreness, which then results in more immune cell recruitment causing the bigger picture symptoms of fever and fatigue," says Hwang.


Starting With the Least Frequent…You May Have Joint Pain

man with dark hair suffering from elbow pain outdoor

Joint pain is common after getting the vaccine, particularly after the second shot. If you experience pain, the CDC recommends taking an over-the-counter pain reliever. Don't take a pain reliever before getting the shot, though; experts aren't sure if that might compromise the vaccine's effectiveness.


You May Have Chills


Chills, like fever, are a common immune response as the body tries to raise its temperature to fight off an invader. As with the other side effects, experts advise drinking plenty of fluids and allowing yourself to rest.


You May Have Muscle Aches

Woman's hands hold back spine suffering pain wear.

Post-vaccine muscle pain may be uncomfortable, but it usually resolves within a day or two. Don't let your fear of side effects dissuade you from getting the shot. "We are willing to tolerate discomfort in other aspects of our life — many people exercise and have muscle aches afterward, and don't say, 'I'm never going to exercise again,'" Dr. William Moss, executive director of the International Vaccine Access Center at the Johns Hopkins Bloomberg School of Public Health, recently told AARP. "There are just many aspects of our lives where we need to be willing to make the trade-off of some degree of discomfort for a longer-term gain."


You May Develop a Headache

Mature man with bad headache at home

Headache has been a commonly reported side effect of all three currently approved COVID vaccines. Most are mild to moderate and don't last long. As with other body aches, over-the-counter pain relievers can help. 


You May Feel Fatigue

Sick young woman lying in the bed covered with blanket

Dr. Anthony Fauci, the nation's top infectious disease expert and chief medical adviser to President Biden, said he experienced fatigue for about a day after getting his second Moderna shot. "I was hoping that I wouldn't get too knocked out. I did for about 24 hours. Now I'm fine," he told the press two days after getting the vaccine. After his first shot, Fauci said he only experienced arm soreness. It's common for side effects to be more pronounced after the second shot, as the immune system is really ramping up. 


And the Most Common Side Effect: You May Feel Injection Site Pain

A man experiencing discomfort in his upper arm

As with any shot, tenderness at the injection site is common after the COVID vaccine. Over-the-counter pain relievers and an ice pack can help. You only need to contact your doctor if the pain increases after 24 hours, or if your side effects don't go away after a few days. 

How to Survive This Pandemic

Woman with face protective mask

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
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