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This is the #1 Sign Your COVID Vaccine is Working

What to expect after you get your shot.

The minor side effects some people experience after getting a COVID vaccine aren't to be feared, experts say. They're actually a sign the shot is working as it should. 

"The vaccine, because you're giving it in the arm, it gives a systemic reaction. You know that because sometimes after the second dose you feel a little achy, a little chilly, which means the immune system is really getting revved up," said Dr. Anthony Fauci, the nation's leading infectious disease expert and chief medical adviser to President Biden, in an interview with MSNBC.

The vaccines work by teaching the immune system to recognize and produce antibodies against the COVID-19 spike protein, which latches onto the body's cells. The disabled protein prevents the virus from replicating exponentially and causing illness. 

It's that process that may trigger side effects in some people. According to the CDC, the most common reported side effects of the COVID vaccine include pain, redness or swelling at the injection site; fatigue; headache; muscle pain; fever; chills; and nausea. (On the other side of the coin, not having side effects does not indicate that the vaccine isn't effective.) 

Fauci said he had experienced fatigue and some minor body aches and chills after his second dose of the Moderna vaccine, but they were gone in little more than a day. Some people experience stronger side effects after the second shot of a two-dose regimen, because the immune system recognizes the invader it was introduced to in the first shot and rallies to fight it off, raising the body's temperature and causing a fever, or triggering inflammation that can manifest as body aches or fatigue. 

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This Means "A Very Robust Immune Response"

One interesting side effect is "COVID arm," which has been reported in several people who received the Moderna vaccine and a handful of people who got the Pfizer jab. It usually takes the form of a red rash that appears a week (or more) after the vaccine is given.   

That's nothing to be concerned about, experts say; in fact, it's a sign that the vaccine is working optimally. "The COVID arm, basically, this is not an unusual reaction to the vaccine," Charles Webb, MD, an allergist-immunologist in Boise, Idaho, told Idaho 6 News. "It just is reflecting that we have a very robust immune response meaning your immune system is recognizing what we injected you with."

If you have side effects like fever or fatigue, the CDC recommends drinking plenty of fluids and getting rest. The agency advises that a sore arm can be remedied with a cool, wet compress and use or exercise. Webb said a rash can be treated with an antihistamine like diphenhydramine (Benadryl) and pain with acetaminophen (Tylenol). 

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How to Survive This Pandemic

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. Read more about Michael