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

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

Symptoms of what is commonly referred to as the COVID arm include redness, swelling and tenderness at the injection site that develops eight days or more 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 Moderna mRNA vaccine, the researchers found that the reaction usually went away after four or five days.

To put this in perspective, the researchers note that about 84% of people in the trials had a reaction, such as pain, shortly after being injected at the injection site. But only 0.8% of people (244 out of about 30,000) experienced these delayed skin reactions after their first dose. But the researchers note that the data from the trial does not provide a complete picture of what these reactions might include and does not differentiate between reactions after the first and second doses of the vaccine.

The researchers therefore looked at 12 case reports of people who developed delayed skin reactions after receiving the Moderna vaccine. Most people noted that their symptoms started on the eighth or ninth day after receiving the first dose of the vaccine, but one person’s reaction started on day four and another developed on day 11. more often, these patients reported itching, redness, swelling, and pain. But it is interesting to note that not all of those who developed this reaction after the first dose also had one after the second: Of the 12 patients in this study, only half reported having a similar reaction after the first dose. second dose (three of them had milder reactions the second time).

While the researchers are still not sure exactly what is causing this reaction, this symptom pattern and a skin biopsy from another patient (who was not one of the 12 others in the study), give them clues. . The biopsy suggests that the body’s T cells, a type of immune cell that can limit the effects of an invading virus, could be the cause of these delayed hypersensitivity reactions.

Perhaps the biggest benefit of these results is that just having one of these delayed reactions to the first dose of a COVID-19 vaccine doesn’t mean you can’t get the second. “We can now reassure you that you can safely get the second #modernavaccine even if you had a significant local # skin reaction that was delayed on the first try”, Esther E. Freeman, MD, Ph.D., director of global health dermatology at Massachusetts General Hospital, associate professor of dermatology at Harvard Medical School and one of the study authors, wrote on Twitter.