Efficacy and viral dynamics of tecovirimat in patients with MPOX: A multicenter open-label, double-arm trial in Japan.

Introduction: Tecovirimat's application in treating mpox remains under-researched, leaving gaps in clinical and virological understanding.

Methods: The Tecopox study in Japan evaluated the efficacy and safety of tecovirimat in patients with smallpox or mpox, who were divided into oral tecovirimat and control groups. Patients with mpox enrolled between June 28, 2022, and April 30, 2023, were included. Demographic and clinical details along with blood, urine, pharyngeal swab, and skin lesion samples were gathered for viral analysis. A multivariable Tobit regression model was employed to identify factors influencing prolonged viral detection.

Results: Nineteen patients were allocated to the tecovirimat group, and no patients were allocated to the control group. The median age was 38.5 years, and all patients were males. Ten patients (52.6%) were infected with human immunodeficiency virus (HIV). Sixteen patients (84.2%) had severe disease. Nine of the 15 patients (60.0%) (four patients withdrew before day 14) had negative PCR results for skin lesion specimens 14 days after inclusion. The mortality rates were 0% on days 14 and 30. No severe adverse events were reported. HIV status and the number of days from symptom onset to tecovirimat administration were associated with lower Ct values (p = 0.027 and p < 0.001, respectively). The median number of days when PCR testing did not detect the mpox virus in each patient was 19.5 days.

Conclusion: Early tecovirimat administration might reduce viral shedding duration, thereby mitigating infection spread. Moreover, patients infected with HIV showed prolonged viral shedding, increasing the transmission risk compared to those without HIV.