What is ‘COVID Arm’? Researchers are finally starting to understand this side effect of the vaccine

If you received the COVID-19 vaccine and developed a swollen, red rash at the injection site several days later, then you may have received the “COVID arm”. This irritating (but harmless) side effect of the coronavirus vaccine is something that researchers are beginning to understand a little better.

Symptoms of what is colloquially known as the COVID arm include redness, swelling and tenderness at the injection site that develop eight or more days after receiving the vaccine, according to a new report in the New England Journal of Medicine. Looking at data from phase 3 clinical trials for the Modern mRNA vaccine, the researchers found that the reaction usually disappeared after four or five days.

To put this in perspective, the researchers note that about 84% of people in the tests had a reaction, such as pain, right after the injection at the injection site. But only 0.8% of people (244 out of about 30,000) had these skin reactions delayed after the first dose. But the researchers note that the trial data do not provide a complete picture of what these reactions may include and do not differentiate the reactions after the first and second doses of the vaccine.

Therefore, the researchers examined 12 case reports of people who developed late skin reactions after receiving the Modern vaccine. Most people noticed that their symptoms started on the eighth or ninth day after receiving the first dose of the vaccine, but one person’s reaction appeared on day four and the other person developed it on day 11. More often, these patients reported itching, redness , swelling and pain. But interestingly, not everyone who developed this reaction after the first dose also received one after the second: Of the 12 patients in this study, only half reported having a similar reaction after the second dose (three of them had milder reactions in the second time around ).

Although the researchers still do not know exactly what is causing this reaction, this pattern of symptoms and a skin biopsy from another patient (who was not one of the other 12 in the study) gives them some clues. The biopsy suggests that the body’s T cells, a type of immune cell that can limit the effects of an invading virus, may be behind these delayed hypersensitivity reactions.

Perhaps the biggest conclusion of these results is that having one of these delayed reactions to the first dose of a COVID-19 vaccine does not mean that you cannot obtain the second. “Now we can guarantee that it is safe to get the second #modernavacin, even if you had a major local reaction #skin delayed with the first injection,” Esther E. Freeman, MD, Ph.D., director of global health dermatology at O ​​Massachusetts General Hospital, an associate professor of dermatology at Harvard Medical School and one of the study’s authors, wrote on twitter.