Incidence of Severe Illness in Pediatric Influenza Outpatients Treated with Baloxavir or Neuraminidase Inhibitors

Introduction: A single oral dose of baloxavir marboxil, a cap-dependent endonuclease inhibitor, is approved for patients with influenza A or B infection; however, real-world evidence is limited. We evaluated the effectiveness of baloxavir vs neuraminidase inhibitors in reducing the incidence of severe illness in influenza outpatients aged 5-11 years.

Methods: In this retrospective cohort study, we analyzed individual-level data from patients treated with these antivirals, using a large, Japanese health insurance claims database (JMDC). Patients were included at the first date of diagnosis of the influenza virus infection (Day 1) in two influenza seasons. The primary outcome was the incidence of hospitalization from Day 2-14.

Results: Of 196,749 included patients (Season 2018/2019, n=103,709; Season 2019/2020, n=93,040), 20.9% received baloxavir, 38.8% received oseltamivir, 28.7% received laninamivir, and 11.6% received zanamivir. In each treatment group, 61-70% patients had influenza A. The incidence of hospitalization from Day 2-14 was significantly lower for baloxavir than for oseltamivir, laninamivir, and zanamivir. The adjusted risk ratio (95% CI) for oseltamivir, laninamivir, and zanamivir were 1.86 (1.30-2.68), 2.11 (1.37-3.25), and 1.90 (1.31-2.77), respectively, compared with baloxavir. Comparative incidence of hospitalizations between agents were unaffected by season or virus type.

Conclusion: Using a large, Japanese health insurance claims database, a lower rate of hospitalization was demonstrated in children aged 5-11 years with an influenza virus infection when treated with baloxavir vs neuraminidase inhibitors. Thus, single dose, oral baloxavir may reduce the incidence of severe illness in these patients.