What To Know About 'COVID Arm'

As with most vaccines, the COVID-19 injection comes with a few less-than-desirable side effects, per the Centers for Disease Control and Prevention (CDC), like pain or swelling at the injection site, fatigue, chills, body aches, or headaches.

Another reported side effect, specifically for Moderna's and Pfizer's COVID-19 vaccines, is a large, red lesion around the injection site, according to an April 2021 study published in The Journal of Allergy and Clinical Immunology.

The side effect has been dubbed "COVID arm," according to the CDC, but it also has a more medically-accurate label: delayed cutaneous hypersensitivity, which essentially means a delayed reaction on the skin.

Here's more about the side effect—and why it shouldn't prevent you from getting your COVID-19 shot.

Why Does COVID Arm Happen—And What Makes It an Unusual Side Effect?

COVID arm appears to be the body's immune system response to the vaccine.

"It seems to be an allergic reaction—a skin reaction that occurs after getting an injection," board-certified dermatologist Debra Jaliman, MD, who has a private practice in Manhattan, NYC, told Health. "We see firmness and redness at the site where the injection occurred." Some people who've experienced COVID arm also report itching and say the lesion is painful to touch.

The interesting thing about COVID arm is that it doesn't appear right away. "Typically, it shows up five to nine days after the first shot," Dr. Jaliman said. That makes it different from most vaccine side effects, which usually occur within a day or two.

COVID arm reportedly lasted up to 21 days for some individuals who were administered the Moderna vaccine, per a JAMA Dermatology article published in May 2021.

Still, COVID arm is generally a brief, harmless response. According to Dr. Jaliman, "[the rash] should go away within 24 hours to a week"—with three to four days being the most common time it takes to subside.

What Else To Know About COVID Arm

The COVID-19 arm reaction has reportedly shown up more in women. For example, 95.4% of women who had had COVID-19 vaccinations reportedly had COVID arm, according to a British Journal of Dermatology study published in September 2021. Still, the association there is unclear as well.

Furthermore, the delayed reaction shouldn't prevent people from getting additional shots, Dr. Jaliman said, recommending that people get subsequent shots in the other arm.

To help ease the itching, Dr. Jaliman suggested an antihistamine like Benadryl, or a topical steroid, adding that ice would help reduce the swelling too. Because it's not an infection, treatment would not include antibiotics.

But if the symptoms last any more than a week, or you experience swelling or pain anywhere else in your body, make an appointment with your healthcare provider just to be on the safe side.

In the event that you do go see your healthcare provider for potential COVID arm, make sure you tell them that you recently had your shot to help with the accuracy of your diagnosis. A June 2021 Journal of Primary Care & Community Health study found that some cases of COVID arm had been misdiagnosed as cellulitis, a serious bacterial infection that requires medical attention.

If you experience any side effects at all after your vaccine, you're also encouraged to report them to either of the CDC's vaccine safety and tracking systems: the Vaccine Adverse Event Reporting System (VAERS) or V-safe.

A Quick Review

There are some side effects of COVID-19 vaccinations, including COVID arm or delayed cutaneous hypersensitivity. It's considered one of the body's immune responses but can show up days after the vaccination is given. Still, COVID arm is typically short-lived and harmless, and treatment might entail using an antihistamine, topical steroid, or ice. Ultimately, it's not a side effect that should keep you from getting a COVID-19 vaccine.