Shanghai Ark Biopharmaceutical Co Ltd (ArkBio) a China-based biopharmaceutical company, announced on Friday that the US Food and Drug Administration (FDA) has approved ziresovir (AK0529) for a phase II clinical trial in the severely ill RSV infected infant patients, including the ones in paediatric intensive care unit (PICU).

Ziresovir is claimed to be is the first direct RSV antiviral drug to successfully complete a phase III clinical trial with positive results. The company says that the clinical study in 1-24 months age patients conducted in China demonstrated that ziresovir can significantly reduce viral load, accelerate the resolution of respiratory symptoms, and significantly lower the risk of recurrent wheezing and asthma over 24-month follow-up period, with a favourable safety profile. Key findings from the clinical study have been published in The New England Journal of Medicine and The Lancet Child & Adolescent Health.

In 2025, ziresovir was included as the only therapeutic drug in the WHO's Paediatric Drug Optimization for Respiratory Syncytial Virus publication. According to ArkBio, the newly approved phase II clinical trial marks the extension of ziresovir's clinical development into the most critically ill RSV patients, representing a key milestone in the clinical development of ziresovir globally.

The company says that the approved multicentre, randomised, double-blind, placebo-controlled phase II clinical trial will focus on severely ill RSV infected infants requiring hospitalisation in PICU, one of the most critical RSV patient populations with the most urgent clinical treatment needs. This clinical trial is designed to evaluate clinical efficacy of ziresovir, especially the length of oxygen treatment and sustained recovery time, providing the clinical basis for the future registrational trials.