Delayed Local Reactions to Moderna COVID-19 Vaccine of Little Consequence

By David Douglas

May 21, 2021

NEW YORK (Reuters Health) - Localized cutaneous reactions delayed for a median of seven days after receiving Moderna COVID-19 vaccine resolve quickly and lead to no further consequences, according to a new U.S. case series.

"The primary take-home message is that delayed localized reactions to the Moderna vaccine are benign, self-limited, and are not a reason to avoid the vaccine," Dr. Alicia J. Little of Yale School of Medicine, in Newhaven, told Reuters Health by email.

She and her colleagues reviewed data on 16 patients who had been referred to Yale New Haven Hospital's Dermatology Services with localized cutaneous injection-site reactions following receipt of Moderna COVID-19 vaccine in January and February.

The patients had a median age of 38 years, most (13) were women and all but two described themselves as being white, the authors report in JAMA Dermatology. The reactions took place between two and 12 days (median, seven days) after receiving the vaccine. They were at or near the injection site and were described as pruritic, painful and edematous pink plaques.

Of the 15 participants who developed localized cutaneous reactions after the first dose, 11 had a similar localized injection-site reaction to the second vaccine dose. Of these, 10 developed the second reaction sooner than the first.

Findings of a histologic examination of a skin-punch-biopsy specimen from one patients following a second-dose reaction "demonstrated mild predominantly perivascular and focal interstitial mixed infiltrate with lymphocytes and eosinophils consistent with a dermal hypersensitivity reaction," the authors note.

"Initially, some people were surprised to develop a rash at the site of injection a week or more after their vaccination, but we and others have found that this side effect is not dangerous," Dr. Little said. "Overall, the reaction may cause a little inconvenience, but it's a small price to pay for being protected from coronavirus."

She added, "The findings in our case series are similar to those reported nationally, both in the popular press as well as in the literature."

Although slightly more subjects developed a reaction to the second dose than had been previously reported, as seen in research, "if second dose reactions occurred, they occurred sooner and were shorter-lived than the first dose reactions. Importantly, no serious vaccine adverse events occurred in association with these delayed localized vaccine reactions."

Dr. Richard Gallo, chairman of the department of dermatology at the University of California, San Diego, who was not involved in the research, told Reuters Health by email, "This is an important study that carefully looked at the local immune reaction after mRNA vaccine. Although local skin reactions after vaccination are to be expected, the relatively new nature of mRNA technology left a gap in understanding if this method of vaccination would create a different response. Importantly, the findings show a type of immune reaction that is localized. It was not the type more associated with severe anaphylaxis."

Dr. Gallo concluded, "These findings are consistent with the overall experience of health care with the vaccine, but the study is limited by the very small number of people (16) that were carefully evaluated."

SOURCE: JAMA Dermatology, online May 12, 2021.