Some People Are Getting a Large (but Harmless) Arm Rash a Week After the COVID-19 Vaccine
A small number of people are reporting a delayed arm rash about a week after receiving the COVID-19 vaccine, most commonly after the first dose.
It’s been dubbed “COVID arm,” but medical professionals refer to it as “delayed cutaneous hypersensitivity.”
The red rash and arm soreness can be annoying and slightly uncomfortable, but experts say it’s harmless and resolves on its own. It should not stop people from getting the second dose of the vaccine.
Vaccines unquestionably save lives, but their disease-fighting power also comes with a potential risk for mild side effects. Even though this can be slightly uncomfortable and annoying, side effects are typically a good thing—it means the vaccine is doing what it’s supposed to do.
The COVID-19 vaccine is no exception. Both the Pfizer-BioNTech and Moderna vaccines can spur flu-like symptoms—like a fever, chills, headache, or fatigue–in some people, a totally normal sign that the body’s immune system is building up those important coronavirus-fighting antibodies, so you can fight off illness in the future should you get infected.
But there’s one post-vaccine reaction that’s suddenly got people talking. While it’s been dubbed “COVID arm,” medical professionals refer to it as “delayed cutaneous hypersensitivity.” It refers to a delayed red rash or lesion that some people develop in their arm around the injection site after receiving the vaccine. It can become itchy, swollen, sore, or slightly painful, but usually just goes away on its own.
While it’s rare, doctors say they’re increasingly noticing this delayed reaction. Here’s what you should know if it happens to you—and why it’s not much to worry about.
What is this delayed arm rash after the vaccine?
Any vaccine can cause pain, redness, or swelling at the injection site a day or two after you get the shot, including the Moderna and Pfizer COVID-19 vaccines.
However, the reaction that has been dubbed as “COVID arm” is unique because it appears about a week after a person gets the vaccine, most commonly after the first dose. “This is a localized reaction with redness, pain, tenderness, and swelling at the injection site that occurs—on average—seven to 10 days after vaccination,” says Hana El Sahly, M.D., an associate professor of molecular virology and microbiology at Baylor College of Medicine in Houston and a national co-principal investigator of the phase 3 clinical trial for the Moderna vaccine. The skin rash can vary in size and shape, but can be as large as 6 inches across.
But it doesn’t seem to be very common. Dr. El Sahly says that it only happens in “a small fraction” of people. Research from her team found that a delayed injection site reaction occurred in less than 1% of participants (244 people) after the first dose of the Moderna vaccine and only 0.2% participants (68 people) after the second dose.
The delayed arm reaction was initially only detected in people who received the Moderna vaccine, but experts confirm the rash is possible with the Pfizer vaccine, too. “While most cases of delayed cutaneous hypersensitivity have been recorded in patients who received the Moderna vaccine, a few cases have been reported by recipients of the Pfizer vaccine,” says Esther Freeman, M.D., Ph.D., director of Global Health Dermatology at Massachusetts General Hospital and principal investigator for the global COVID-19 Dermatology Registry.
What causes a delayed arm rash after the Moderna vaccine?
William Schaffner, M.D., an infectious disease specialist and professor at the Vanderbilt University School of Medicine believes it probably comes down to the root cause of most vaccine side effects. It’s the “beginning of the body’s immune response interacting with the vaccine,” he says.
Some experts believe that it could be a minor allergic reaction, but it’s not entirely clear why it happens in a small group of people but not others, Dr. El Sahly says, noting that researchers are looking into it. “We are trying to obtain a biopsy and have a better description of this reaction,” she says.
Is an arm rash after the COVID-19 vaccine something to worry about? How long does it last?
Doctors aren’t overly concerned about this. While Dr. Schaffner admits that it can be annoying—“it bothers people when it happens”—he says acknowledging in advance that you could get a delayed arm rash might help reduce the worry if the side effect actually surfaces.
Overall, you really shouldn’t stress about it, as the reaction often goes away “within a few days” after it appears, says Dr. El Sahly. Specifically, the study mentioned above found that it typically resolved in participants within four to five days. It’s “rarely” linked with side effects in other areas of the body, like a headache or fever, Dr. Sahly says.
Above all, if you do happen to experience the delayed arm rash, it should not stop you from getting your second dose of the vaccine. While it might be bothersome for a few days, it will go away—and COVID-19 is much more of a threat.
How to soothe an arm rash or relieve arm soreness after the COVID-19 vaccine
If your arm hurts, Dr. El Sahly recommends taking a non-steroidal anti-inflammatory medication like ibuprofen (per the bottle’s dosage instructions), which should help minimize the pain.
If it itches, the experts we talked to suggest taking an antihistamine (like Benadryl), applying an OTC hydrocortisone cream, or using a cool compress for added relief.
This delayed arm reaction should resolve fairly quickly, but if your rash persists for longer than a week, it’s not at or close to the injection site, or you have more general symptoms that aren’t getting better, Dr. El Sahly says it’s a good idea to call your doctor about next steps, just to be on the safe side.
The CDC also encourages you to report any COVID-19 vaccine reactions to its V-safe After Vaccination Health Checker.
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