Histopathological analysis of skin reactions after coronavirus disease 2019 vaccination: Increment in number of infiltrated plasmacytoid dendritic cell.

Skin disorders are frequent adverse events after coronavirus disease 2019 (COVID-19) vaccination. However, the pathogenesis of these disorders is not fully understood. Here, we report a case series of cutaneous adverse events following COVID-19 vaccination, and the results of our investigation reveal the underlying mechanism. Case 1: a 47-year-old female developed a wheal, confined to the COVID-19 vaccination site, 2 days after her first injection. She was treated with topical steroids and oral antihistamines. Case 2: a 51-year-old female showed generalized petechial erythema accompanied by fever, genital bleeding, thrombocytopenia, liver dysfunction, and disseminated intravascular coagulation, 2 days after her second injection. She was diagnosed with vaccine-induced macrophage activation syndrome and treated with anti-inflammatory therapy. Immunohistological analysis of the skin eruption, in both these cases, showed infiltration of CD123+ BDCA2+ plasmacytoid dendritic cells (p-DC). Despite the distinctive clinical features in these two cases, this finding suggests that p-DC might be involved in different cutaneous adverse events after COVID-19 vaccination.