Inhaled Zanamivir vs Oral Oseltamivir to Prevent Influenza-related Hospitalization or Death: A Nationwide Population-based Quasi-experimental Study

Abstract

Abstract Background Meta-analyses of individual patient data from randomized, controlled trials show that early oseltamivir treatment for influenza cut the risk of pneumonia and hospitalization by 44% and 63%, respectively. However, data on the effectiveness of inhaled zanamivir in preventing hospitalization and death are lacking. Methods This nationwide, population-based, cohort study included all outpatients treated with inhaled zanamivir or oral oseltamivir within 48 hours after a clinical diagnosis of influenza before and after the rollout of inhaled zanamivir as the first-line antiviral in Taiwan. The main outcome was influenza-related hospitalization or death within 14 days. Those who developed the outcome within 2 days were excluded from analyses. Propensity score stratification was used to control confounding from covariates. Results A total of 865 032 eligible influenza outpatients were included in the analysis. The risk of developing the main outcome (adjusted hazard ratio [aHR], 1.01; 95% confidence interval [CI], .96 to 1.06) did not differ between the inhaled zanamivir group (n = 595 897, 68.9%, the reference) and the oral oseltamivir group (n = 269 135, 31.1%). Prespecified analysis on high-risk subgroups further showed that inhaled zanamivir is not inferior to oral oseltamivir in either patients aged ≥65 years (aHR, 1.14; 95% CI: 1.05 to 1.25) or patients with chronic lung diseases (aHR, 1.23; 95% CI: 1.08 to 1.41). Conclusions Inhaled zanamivir is not inferior to oral oseltamivir as outpatient treatment in preventing influenza-related hospitalization or death for patients whose conditions do not require hospitalization within 2 days.