Efficacy and safety of ziresovir in hospitalised infants aged 6 months or younger with respiratory syncytial virus infection in China: findings from a phase 3 randomised trial with 24-month follow-up.

Summary

In hospitalized infants ≤6 months with PCR-confirmed RSV, oral ziresovir produced a greater improvement in the Wang bronchiolitis clinical score at day 3 versus placebo (LS mean difference −1.2, p=0.0004) with no drug-related serious adverse events. This prespecified subgroup analysis demonstrates early clinical benefit and a favorable safety profile over a 5-day treatment window with 24 months of follow-up.

Key Findings

• At day 3, ziresovir improved WBCS more than placebo (LS mean change −3.5 vs −2.2; difference −1.2; p=0.0004) in the ITT-infected population ≤6 months.
• No drug-related serious adverse events or deaths occurred; drug-related TEAEs were 18% (ziresovir) vs 11% (placebo).
• Trial included 24-month safety follow-up; the prespecified infant subgroup analysis supports early symptomatic benefit.

Clinical Implications

Ziresovir may offer an early clinical benefit for hospitalized infants with RSV and a favorable safety profile; larger global trials powered for hard outcomes (oxygen requirement, LOS, ICU) should guide adoption.

Limitations

• Primary endpoint is a short-term clinical score at 48 hours post-baseline, not hard outcomes (e.g., oxygen days, hospitalization length).
• Subgroup limited to infants ≤6 months in China; generalizability and effect in severe disease require confirmation.

Future Directions

Conduct larger, multinational trials powered for clinically meaningful endpoints (oxygen use, LOS, ICU admission, mortality), evaluate resistance, and define optimal timing with supportive care.