In rare cases, people who receive the two-dose Moderna COVID-19 vaccine may experience a red, itchy patch of skin a few days later at the injection site, a new report finds.

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They shouldn't panic: This "COVID arm" reaction, although annoying, was short-lived in all cases and was easily treated with topical steroid creams, according to a team of researchers at Yale University.

"No serious vaccine adverse events occurred in association with these cutaneous [skin] reactions," the team reported, and the side effect is certainly no reason to avoid getting vaccinated against COVID-19.

The study was led by Dr. Alicia Little, an assistant professor of dermatology at the Yale School of Medicine in New Haven, Conn., and published online May 12 in the journal JAMA Dermatology.

In the study, Little's group noted that raised, red and itchy blotches on COVID-19 vaccine recipients' arms have been noted before and dubbed "COVID arm." In the new study, the Yale team took a closer look at 16 such cases diagnosed in people aged 25 to 89 (average age 38).

Most (14) were white and 13 of the 16 patients were women, which was not surprising, the team said, because it's known that women are more vulnerable than men to "hypersensitivity" reactions to vaccines, and they are also more likely to report such side effects to their doctors.

None of the COVID arm reactions arose at the time of vaccination. After the first dose of Moderna vaccine, the skin reaction appeared anywhere from two to 12 days after the shot (average seven days). Most people who had a skin reaction after the first shot also had a reaction after their second dose, typically two or so days after the injection, the study authors noted.

The good news: Treatment was available and most COVID arm cases faded away with an average duration of about three to five days.

"Treatments included topical steroids, oral antihistamines and cool compresses," the researchers said.

No such COVID arm reactions were observed in people who got the Pfizer COVID-19 vaccine, they added.

It's not clear why Moderna vaccinations are more likely to produce the side effect, although Little's group stressed that it is rare: In the clinical trial that led up to the vaccine's approval, 312 such cases were noted out of more than 30,000 participants enrolled.

Dr. Michele Green is a dermatologist at Lenox Hill Hospital in New York City. Reading over the report, she concurred that she has "seen several cases of these delayed hypersensitivity reactions after the Moderna COVID-19 vaccine."

"These reactions have presented as localized itchy, red, and sometimes painful plaques near or at the site of injection," Green said, but they've not been associated with any more serious side effects.

"I have found them responsive to topical steroids and resolve in a short amount of time," she added. Two more Moderna COVID vaccine reactions.

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—Ernie Mundell Healthday Reporter