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If you received a COVID-19 vaccine and developed a swollen red rash at the injection site a few days later, then you may have received the “COVID arm”. This annoying (but ultimately harmless) side effect of the coronavirus vaccine is something that researchers are now beginning to understand a little better.
Symptoms of what is colloquially known as the COVID arm include redness, swelling, and sensitivity at the injection site that develops eight or more days after the vaccine is given, according to a new report from New England Journal of Medicine. Regarding the phase 3 data from clinical trials for the Modern mRNA vaccine, the researchers found that the reaction usually disappeared after four or five days.
To put this into perspective, the researchers note that about 84% of those in the study had a reaction, such as pain, shortly after being shot at the injection site. But only 0.8% of people (244 out of about 30,000) had these delayed skin reactions after their first dose. However, the researchers note that the study data do not provide a complete picture of what these reactions might include and do not differentiate reactions after the first and second dose of vaccine.
Thus, the researchers examined 12 case reports of people who developed delayed skin reactions after receiving the Moderna vaccine. Most people noticed that their symptoms started on day eight or nine after the first dose of vaccine, but one person’s reaction occurred on the fourth day and one occurred on day 11. Most commonly, these patients reported itching, redness. , swelling and pain. Interestingly, not all who developed this reaction after the first dose received one after the second: of the 12 patients in this study, only half reported receiving a similar reaction after the second dose. (three of those who showed milder reactions over time).
Although researchers still don’t know exactly what causes this reaction, this type of symptom and a skin biopsy from another patient (who was not one of the other 12 in the study) give 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 solution to 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 get a second one. “We can now make sure it’s safe to get the second modern vaccine, even if you had a delayed local # skin reaction on the first shot,” Esther E. Freeman, MD, Ph.D., director of dermatology Massachusetts General Hospital, associate professor of dermatology at Harvard Medical School and one of the study’s authors, wrote on Twitter.