Shanghai Ark Biopharmaceutical Co., Ltd. announced that the U.S. 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 pediatric intensive care unit (PICU).

Severe RSV Infection: An Urgent Unmet Need in PICU

RSV is the leading pathogen of lower respiratory tract infections (LRTIs) in infants and young children globally, causing approximately 33 million LRTI cases, 3.6 million hospitalizations, and more than 100,000 deaths annually. Severely ill RSV infected infants often require admission to the PICU for intensive care such as respiratory support, with rapid disease progression, high risk and a heavy medical burden. There is currently no approved RSV-specific antiviral therapy worldwide; clinical management remains limited to symptomatic and supportive care, such as oxygenation, leaving an urgent unmet need for effective antiviral treatment in hospitalized RSV infected patients with severe diseases.

Ziresovir Advances to Treat Severely Infected Infant Patients

Ziresovir is the first direct RSV antiviral drug to successfully complete a phase III clinical trial with positive results. 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 favorable 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. 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.

FDA Approved Phase II Clinical Trial

The approved multicenter, randomized, double-blind, placebo-controlled phase II clinical trial will focus on severely ill RSV infected infants requiring hospitalization 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.