Baloxavir Marboxil in Chinese Pediatric Patients Aged 1 to < 5 Years with Influenza: Safety and Clinical and Virologic Outcomes

INTRODUCTION: Baloxavir marboxil (baloxavir), a cap-dependent endonuclease inhibitor, has been proven safe and efficacious against influenza and approved for the treatment of influenza in children aged ≥ 5 years in China. There were limited data on baloxavir in Chinese pediatric patients aged 1 to < 5 years with influenza. This study aimed to evaluate the safety, clinical efficacy, and virologic outcomes of baloxavir for treating influenza in this younger age group. METHODS: In this single-arm, multicenter trial, patients received a single oral dose of baloxavir (2 mg/kg for participants weighing < 20 kg, or 40 mg for participants weighing ≥ 20 kg to < 80 kg). The primary endpoint was safety. Efficacy, virology, and palatability endpoints were also assessed. RESULTS: All 100 enrolled children completed the study and received baloxavir. Adverse events were reported in 29 (29.0%) children, most commonly bronchitis and diarrhea. No death or adverse events leading to discontinuation occurred. Eighty children were included in the clinical efficacy and virologic assessment. The median [95% confidence interval (CI)] time to resolution of influenza signs and symptoms was 150.17 (90.23, NE) h. The median duration of fever was 38.65 (95% CI 25.32, 42.35) h. Infectious virus titers rapidly declined by day 2 post-dose. The proportion of subjects with a positive viral titer was reduced to 8.7% at this timepoint. Of the 100 children enrolled, more than 70% of children rated baloxavir as favorable in the palatability test. CONCLUSION: A single, oral dose of baloxavir was well-tolerated in Chinese children aged 1 to < 5 years, with rapid influenza virus clearance and associated symptom alleviation, suggesting baloxavir was an important treatment option for Chinese pediatric patients with influenza. TRIAL REGISTRATION: The study was registered at the Chinese Clinical Trial Registry (ChiCTR) on March 14, 2025 (registration no. ChiCTR2500098911); Retrospectively registered.