‘Covid Arm’ Rash After the Moderna Shot Is Common but Not Worrisome
Reactions frequently occur after vaccines while the immune system is doing its thing
About five days after I got my Moderna vaccine, I found myself scratching the place where I’d gotten it. At first it was automatic, like scratching any itch, but soon I realized it was really itchy — and big and warm and red. I knew there could be injection site reactions, but with all my past vaccines, it had only been red or swollen at the injection site for a day or two after the shot. This was a week later, which seemed weird.
It turns out it isn’t as weird as I thought, and it’s something many others, though mostly women it seems, are experiencing as well.
“I was concerned that I might be having some kind of allergic reaction, so I posted this picture and asked if I should contact my doctor,” said Amanda (last name withheld by request), who experienced it after her first dose. But her friends and the nurse who gave her the second dose said it wasn’t anything to worry about.
These reactions were reported in the clinical trials but only rarely: 0.8% of participants reported one after the first dose and 0.2% after the second dose. The formal term is delayed cutaneous hypersensitivity — a type of minor allergic immune response that can occur after other drugs as well — but many are just calling it “Covid arm.” (I find this ironic since it’s more like “anti-Covid arm” if it’s from a vaccine!)
A case series of 12 people reported in a letter to the New England Journal of Medicine March 3 found evidence that the hypersensitivity results from activation of T cells, the immune cell type that trains B cells to build antibodies and that causes virus-infected cells to self-destruct. That’s good news because it suggests the vaccine brings about immunity through T cells as well as antibodies. That also may explain why it takes longer — four to 11…