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If you received a vaccine against COVID-19 and developed a swollen red rash at the injection site several days later, you may have received the “COVID arm”. This annoying (but ultimately harmless) side effect of the coronavirus vaccine is something 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 develop eight or more days after the vaccine, according to a new report published in the New England Journal of Medicine. Looking at the data from the phase 3 clinical trials of the Modern 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 the shot at the injection site. But only 0.8% of people (244 out of about 30,000) experienced these delayed skin reactions after the first dose. But the researchers note that the trial data do not provide a complete picture of what these reactions might include and do not differentiate between reactions after the first and second doses of the vaccine.
Thus, the researchers examined 12 case reports of people who developed delayed skin reactions after receiving the Modern vaccine. Most people noted that their symptoms began 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 developed it on day 11. The most common of these patients is itching, redness, swelling and pain. But, interestingly, not everyone who developed this reaction after the first dose also got one after the second: of the 12 patients in this study, only half reported having a similar reaction after the second dose. (three of these experienced milder reactions the second). time).
Although researchers still don’t know exactly what causes this reaction, this pattern of symptoms and a biopsy of another patient’s skin (which 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 invasive virus, may be behind these delayed hypersensitivity reactions.
Perhaps the most important result 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 get the second. “We can now make sure it’s safe to get the second #modern vaccine, even if you have a large delayed # local skin reaction on the first shot,” said 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’s authors, wrote on Twitter.