Favipiravir Is Associated With Reduced 28‐Day Mortality in Severe Fever With Thrombocytopenia Syndrome: A Multicenter Propensity Score–Matched Study

ABSTRACT This study aimed to evaluate the efficacy of add‐on favipiravir to standard ribavirin therapy in reducing 28‐day mortality among patients with SFTS and to identify clinical subgroups that may derive greater benefit. This multicenter retrospective study included adults with laboratory‐confirmed SFTS from four hospitals (2022–2025). All patients received standard ribavirin therapy, while patients in the FPV group additionally received favipiravir at admission. Propensity score matching ensured balance in baseline characteristics. Survival was analyzed using Kaplan–Meier curves and Cox models with subgroup interaction analyses. Among 1199 eligible patients, the 28‐day mortality was 20.6%. The FPV group showed lower 28‐day mortality than the non‐FPV group (14.1% vs. 24.5%). FPV treatment was associated with lower 28‐day mortality across all baseline viral load categories, with the most pronounced association observed in patients with low viral load (< 10 5 copies/mL), and a weaker but still significant association in those with high viral load (≥ 10 7 copies/mL). A significant association was also observed in patients with onset‐to‐admission interval ≥ 5 days and in those aged < 70 years. A trend toward lower mortality was also observed in patients with an onset‐to‐admission interval < 5 days and in those aged ≥ 70 years, although the associations were not statistically significant. FPV treatment was associated with reduced mortality regardless of corticosteroid or intravenous immunoglobulin use. In this study, FPV therapy was associated with reduced 28‐day mortality regardless of baseline viral load or the interval of onset‐to‐admission. These findings support initiating FPV therapy promptly after admission without waiting for viral load results.