Clinical course and virologic dynamics of Mpox during tecovirimat treatment: Prospective multicenter case series in Japan

INTRODUCTION: At the time of this study, no approved treatment for mpox was available in Japan, and data on the clinical course and virological changes during tecovirimat treatment were limited. METHODS: We conducted a prospective multicenter observational case series of patients with PCR-confirmed mpox between June 28, 2022, and March 31, 2025, to describe the clinical course and safety of a 14-day course of tecovirimat. Participants could choose treatment or no treatment. RESULTS: All 31 participants received tecovirimat; 24 completed a single 14-day course, and 2 received multiple courses plus vaccinia immune globulin. The median age was 39 years (range, 21-74), and all were men. Nineteen (61.3%) were people living with HIV, with a median CD4 count of 531 cells/μL (range, 50-830), including three with CD4 counts <200 cells/μL. Severe mpox occurred in 23 participants (74.2%), three of whom (9.7%) had risk factors for severe disease, all due to CD4 < 200 cells/μL. Skin lesions were present in 30 participants. At day 14, skin PCR results were available for 23 participants; 16 (69.6%) were negative. No deaths occurred within 14 or 30 days, although one patient with advanced HIV infection died following prolonged hospitalization. Adverse events occurred in 2 participants and were considered unrelated to treatment. DISCUSSION: This prospective multicenter case series describes the clinical course of mpox and temporal dynamics of skin PCR negativity in patients receiving tecovirimat in real-world practice.