Delayed hypersensitivity reactions at the site of injection with the Moderna COVID-19 vaccine are possible, but these delayed reactions do not represent a contraindication to secondary vaccination. This is according to findings from a case series study published in JAMA Dermatology.

The case series study included 16 patients referred to Yale New Haven Hospital with localized cutaneous injection site reactions from January to February 2021. The investigators examined demographic data, relevant medical history, and clinical course. In addition to evaluating these data, the researchers also reviewed photographs of 13 patients and histopathologic examination findings for a skin biopsy taken from 1 of the patients.

The median age of the case series cohort was 38 years, and the majority of patients (81%) were women and self-identified as White (n=14). None of the patients in the study had received the COVID-19 vaccine from Pfizer-BioNTech.


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A total of 15 patients in the series had a reaction to their first dose of the Moderna COVID-19 vaccine. Delayed localized skin reactions occurred at or near the injection site and developed a median of 7 days following vaccination. The cutaneous reactions were described as painful, pruritic, and edematous pink plaques.

The skin biopsy specimen showed mild, predominantly perivascular mixed infiltrate with eosinophils and lymphocytes. According to the investigators, this finding was consistent with findings reported in a dermal hypersensitivity reaction.

Most patients (n=11) experienced a similar localized injection-site reaction to the second dose of the Moderna vaccine. Of these patients, 10 experienced the second reaction much sooner than they did the first dose.

Limitations of this study included its retrospective nature, the single-center design, and the inclusion of a small number of cases from a short period of time.

The researchers concluded that “in contrast to immediate hypersensitivity reactions”that develop more than 4 hours from vaccination, the “delayed localized hypersensitivity reactions are not a contraindication to subsequent vaccination.”

Reference

Johnston MS, Galan A, Watsky KL, Little AJ. Delayed localized hypersensitivity reactions to the Moderna COVID-19 vaccine: A case series. JAMA Dermatol.  Published online May 12, 2021. doi:10.1001/jamadermatol.2021.1214