Clinical and histopathological spectrum of delayed adverse cutaneous reactions following <scp>COVID</scp> ‐19 vaccination

Background As more people become vaccinated against the SARS‐CoV‐2 virus, reports of delayed cutaneous hypersensitivity reactions are beginning to emerge. Methods In this IRB‐approved retrospective case series, biopsy specimens of potential cutaneous adverse reactions from the Pfizer‐BioNTech or Moderna mRNA vaccine were identified and reviewed. Clinical information was obtained through the requisition form, referring clinician, or medical chart review. Results Twelve cases were included. Histopathological features from two injection‐site reactions showed a mixed‐cell infiltrate with eosinophils and a spongiotic dermatitis with eosinophils. Three biopsy specimens came from generalized eruptions that showed interface changes consistent with an exanthematous drug reaction. Three biopsy specimens revealed a predominantly spongiotic pattern, consistent with eczematous dermatitis. Small‐vessel vascular injury was seen in two specimens, which were diagnosed as urticarial vasculitis and leukocytoclastic vasculitis, respectively. There were two cases of new‐onset bullous pemphigoid supported by histopathological examination and direct immunofluorescence studies. Eosinophils were seen in 10 cases. Conclusions Dermatopathologists should be aware of potential cutaneous adverse reactions to mRNA‐based COVID‐19 vaccines. Histopathological patterns include mixed‐cell infiltrates, epidermal spongiosis, and interface changes. Eosinophils are a common finding but are not always present. Direct immunofluorescence studies may be helpful for immune‐mediated cutaneous presentations such as vasculitis or bullous pemphigoid.