Delayed Localized Hypersensitivity Reactions to the Moderna COVID-19 Vaccine: A Case Series | Dermatology | JAMA Dermatology | JAMA Network
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    1 Comment for this article
    Wondering about injection technique
    Francis Holt, PhD, RN |
    In multiple videos of people receiving vaccines, I have seen vaccinators pushing the plunger before the needle is in muscle tissue. I wonder whether or not administration technique has any causal relationship to the results reported here. It is unlikely that this could be controlled for, but the question suggests continuing training in vaccination technique might be a worthwhile step to take.
    Brief Report
    May 12, 2021

    Delayed Localized Hypersensitivity Reactions to the Moderna COVID-19 Vaccine: A Case Series

    Author Affiliations
    • 1Department of Dermatology, Yale University School of Medicine, New Haven, Connecticut
    • 2Department of Pathology, Yale University School of Medicine, New Haven, Connecticut
    JAMA Dermatol. 2021;157(6):716-720. doi:10.1001/jamadermatol.2021.1214
    Key Points

    Question  What are the clinical course and histopathologic examination findings for delayed injection-site reactions to the Moderna coronavirus disease 2019 (COVID-19) vaccine?

    Findings  The Moderna COVID-19 vaccine may cause a delayed localized hypersensitivity reaction with a median latency to onset of 7 days after vaccine administration. This pruritic and variably tender reaction has a median duration of 5 days, but may persist for up to 21 days, and may occur again and sooner after the second vaccine dose; no serious adverse events were observed in association with this cutaneous reaction to the Moderna COVID-19 vaccine.

    Meaning  Self-limited localized delayed hypersensitivity reactions to the Moderna COVID-19 vaccine may occur, and in contrast with immediate hypersensitivity reactions, these delayed hypersensitivity reactions are not a contraindication to subsequent vaccination.


    Importance  In response to the coronavirus disease 2019 (COVID-19) pandemic, 2 mRNA vaccines (Pfizer-BioNTech and Moderna) received emergency use authorization from the US Food and Drug Administration in December 2020. Some patients in the US have developed delayed localized cutaneous vaccine reactions that have been dubbed “COVID arm.”

    Objective  To describe the course of localized cutaneous injection-site reactions to the Moderna COVID-19 vaccine, subsequent reactions to the second vaccine dose, and to characterize the findings of histopathologic examination of the reaction.

    Design, Setting, and Participants  This retrospective case series study was performed at Yale New Haven Hospital, a tertiary medical center in New Haven, Connecticut, with 16 patients referred with localized cutaneous injection-site reactions from January 20 through February 12, 2021.

    Main Outcomes and Measures  We collected each patient’s demographic information, a brief relevant medical history, clinical course, and treatment (if any); and considered the findings of a histopathologic examination of 1 skin biopsy specimen.

    Results  Of 16 patients (median [range] age, 38 [25-89] years; 13 [81%] women), 14 patients self-identified as White and 2 as Asian. The delayed localized cutaneous reactions developed in a median (range) of 7 (2-12) days after receiving the Moderna COVID-19 vaccine. These reactions occurred at or near the injection site and were described as pruritic, painful, and edematous pink plaques. None of the participants had received the Pfizer-BioNTech vaccine. Results of a skin biopsy specimen demonstrated a mild predominantly perivascular mixed infiltrate with lymphocytes and eosinophils, consistent with a dermal hypersensitivity reaction. Of participants who had a reaction to first vaccine dose (15 of 16 patients), most (11 patients) developed a similar localized injection-site reaction to the second vaccine dose; most (10 patients) also developed the second reaction sooner as compared with the first-dose reaction.

    Conclusions and Relevance  Clinical and histopathologic findings of this case series study indicate that the localized injection-site reactions to the Moderna COVID-19 vaccine are a delayed hypersensitivity reaction. These reactions may occur sooner after the second dose, but they are self-limited and not associated with serious vaccine adverse effects. In contrast to immediate hypersensitivity reactions (eg, anaphylaxis, urticaria), these delayed reactions (dubbed “COVID arm”) are not a contraindication to subsequent vaccination.