Here's How to Respond When Moderna Vaccine Recipients Have ‘COVID Arm’

Pharmacists and other healthcare professionals using the Moderna mRNA-1293 vaccine to protect against COVID-19 have been somewhat caught by surprise when patients have reported ‘COVID arm.” The delayed hypersensitivity reaction isn’t a contraindication against the second vaccine dose, however, according to public health officials. Here is how a new study characterizes the response and what can be done to alleviate bothersome symptoms.

BOSTON – Chances are that most pharmacists providing COVID-19 vaccines have been questioned about the significance of what has come to be called “COVID arm,” a delayed hypersensitivity reaction after receiving the Moderna mRNA-1273 vaccine .

A letter to the editor published in the New England Journal of Medicine (NEJM) advises that Phase 3 clinical data from the Moderna vaccine trial showed delayed skin hypersensitivity in a small number of the more than 30,000 trial participants. Yet, according to Massachusetts General Hospital-led authors, the large, red, sometimes raised, itchy or painful skin reactions were never fully characterized or explained. The result is that many healthcare professionals are unprepared to recognize them and guide patients on treatment options and completion of the second dose of the vaccine.

"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," explained Kimberly Blumenthal, MD, MSc, lead author of the letter and 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."

In a series of 12 patients with the reaction, Blumenthal and her co-authors observed that symptom onset ranged from four days after the first dose up to 11 days post-vaccination, with a median onset of symptoms on day eight. While most patients were treated with ice and antihistamines, some required corticosteroids and one was erroneously treated with antibiotics, they said.

"Delayed cutaneous hypersensitivity could be confused - by clinicians and patients alike - with a skin infection," added letter co-author Erica Shenoy, MD, PhD, associate chief of the MGH Infection Control Unit. "These types of reactions, however, are not infectious and thus should not be treated with antibiotics."

Symptoms usually cleared up after nearly a week, although half of the patients experienced a reaction after the second dose at or around 48 hours post-vaccination but none of them had a more severe reaction than the first one. . No patient experienced a dose two reaction that was more severe than their dose one reaction.

"For most people who are experiencing this, we believe it's tied to the body's immune system going to work," said Esther Freeman, MD, PhD, director of Global Health Dermatology at MGH and co-author of the NEJM letter. "Overall, this data is reassuring and should not discourage people from getting the vaccine."

The national Centers for Disease Control and Prevention has advised that vaccine recipients who have the hypersensitivity reaction after the first dose should have the second dose in the other arm.

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