Delayed vaccine skin reaction no cause for alarm,

Changes unpleasant but harmless, not an infection, doctors say.

Some people are having delayed reactions to their first dose of a COVID-19 vaccine, with their arms turning red, sore, itchy and swollen a week or so after the shot.

The reactions, although unpleasant, appear to be harmless. But the angry-looking skin condition can be mistaken for an infection, according to a letter published Wednesday in The New England Journal of Medicine. The doctors said they wanted to share information about the cases to help prevent the needless use of antibiotics and to ease patients’ worries and reassure them that they can safely get their second vaccine shot.

“We modified our patient handout once we started seeing this,” Dr. Kimberly Blumenthal, an author of the letter and an allergist at Massachusetts General Hospital, said in an interview. “We had said it was normal to get redness, itching and swelling when you get the vaccine. We changed the wording to say it can also start seven to 10 days after you get the vaccine.”

The letter describes the experiences of 12 people who had “delayed large local reactions” that began four to 11 days after the first shot of the Moderna vaccine, within a median of eight days. The report is not a controlled study but, rather, a series of cases that came to the doctors’ attention because the vaccine recipients were concerned and wanted to know whether they should get the second shot.

Moderna reported delayed skin reactions in its large clinical trial in 0.8% of recipients after the first dose and 0.2% after the second dose.