Multifocal mucocutaneous herpes simplex virus type 1 infection temporally associated with seasonal influenza vaccination in a young adult without a known immunocompromising condition: A case report.

Seasonal influenza vaccination is widely implemented and generally safe; however, rare immunological adverse events have been reported. We describe a case of multifocal mucocutaneous Herpes simplex virus type 1 (HSV-1) infection temporally associated with seasonal influenza vaccination in a 28-year-old man without a known immunocompromising condition. Seven days after vaccination, he developed oral ulcerative lesions and multiple vesicular eruptions involving the anterior chest wall, pubic region, and penile shaft. A multiplex polymerase chain reaction assay performed on specimens obtained from clinically apparent lesions detected HSV-1 DNA, whereas HSV-2 and other sexually transmitted pathogens included in the assay were not detected. Intravenous acyclovir was administered, resulting in complete clinical resolution. Although causality cannot be established, the close temporal relationship between influenza vaccination and the onset of HSV-1 infection is noteworthy, while alternative explanations cannot be excluded. This case highlights the importance of considering HSV infection in the differential diagnosis of multifocal mucocutaneous lesions occurring after influenza vaccination without implying a causal relationship.