Some people given the Moderna COVID-19 vaccine may develop a reaction at the injection site that can first appear more than a week after they get the shot, research shows.
A minority of patients may experience a large, red, sometimes raised, itchy or painful skin reaction, according to researchers at Massachusetts General Hospital (MGH) in Boston.
Although the reaction was seen in clinical trials, it should not discourage people from getting the Moderna vaccine, they said.
"Whether you've experienced a rash at the injection site right away or this delayed skin reaction, neither condition should prevent you from getting the second dose of the vaccine," said study author Dr. Kimberly Blumenthal. She is co-director of the Clinical Epidemiology Program in the division of rheumatology, allergy and immunology at MGH.
"Our immediate goal is to make physicians and other care providers aware of this possible delayed reaction, so they are not alarmed, but instead well-informed and equipped to advise their patients accordingly," Blumenthal said in a hospital news release.
Blumenthal said her own clinical group has seen and reported on 12 patients with the reactions. Among those, symptoms started between four and 11 days after vaccination.
According to Dr. Erica Shenoy, associate chief of the hospital's infection control unit, this delayed skin reaction "could be confused -- by clinicians and patients alike -- with a skin infection. These types of reactions, however, are not infectious and thus should not be treated with antibiotics."
Symptoms usually cleared up in a week. Of patients in the study, half had a reaction after the second shot -- at or around 48 hours after vaccination. No patient had a reaction to the second dose that was more severe than their reaction to the first shot, the findings showed.
Dr. Esther Freeman is director of Global Health Dermatology at MGH. "For most people who are experiencing this, we believe it's tied to the body's immune system going to work," she said. "Overall, this data is reassuring and should not discourage people from getting the vaccine."
The findings were published online March 3 in the New England Journal of Medicine.
To learn more about COVID-19 vaccines, visit the U.S. Centers for Disease Control and Prevention.
SOURCE: Massachusetts General Hospital, news release, March 3, 2021