Evaluating Ziresovir for the Treatment of Respiratory Syncytial Virus Infection in Infants
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Reviewed & Translated by Dat Tien Nguyen, B.A, ScM.
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Posted on September 24th, 2025
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Respiratory syncytial virus (RSV) is a leading cause of lower respiratory tract infection and hospitalization in infants and young children. Current recommendations advise vaccinating children born during, or about to enter, their first RSV season. However, vaccination is not always feasible, highlighting the need for effective antiviral therapies. To address this gap, a study funded by Shanghai Ark Biopharmaceutical investigated the use of ziresovir in treating RSV infection in young children.
The phase 3 clinical trial, conducted in China, enrolled 188 hospitalized infants with a median age of 3 months. Forty percent of cases were caused by RSV subtype A, while the remainder were subtype B. Coinfection with other viruses occurred in 30% of participants, most commonly rhinovirus. At baseline, disease severity was assessed with the Wang bronchiolitis clinical score, with an average score of 6.8 out of 12, indicating moderate disease.
Participants were randomized to receive either placebo or ziresovir orally every 12 hours, dosed according to body weight: 10 mg for children under 5 kg, 20 mg for those between 5 and 10 kg, and 40 mg for those between 10 and 20 kg. Ziresovir is a direct-acting antiviral that targets the RSV fusion (F) protein, thereby blocking viral entry and replication.
After three days of treatment, children who received ziresovir demonstrated greater clinical improvement, with a mean reduction of 3.5 points in the Wang score compared to 2.2 points in the placebo group. Improvements were consistent across all score components, including respiratory muscle retraction, respiratory rate, and wheezing. Ziresovir treatment was also associated with a significant reduction in viral load. The authors note that future research should include larger cohorts and direct comparisons with other antivirals such as ribavirin.
The phase 3 clinical trial, conducted in China, enrolled 188 hospitalized infants with a median age of 3 months. Forty percent of cases were caused by RSV subtype A, while the remainder were subtype B. Coinfection with other viruses occurred in 30% of participants, most commonly rhinovirus. At baseline, disease severity was assessed with the Wang bronchiolitis clinical score, with an average score of 6.8 out of 12, indicating moderate disease.
Participants were randomized to receive either placebo or ziresovir orally every 12 hours, dosed according to body weight: 10 mg for children under 5 kg, 20 mg for those between 5 and 10 kg, and 40 mg for those between 10 and 20 kg. Ziresovir is a direct-acting antiviral that targets the RSV fusion (F) protein, thereby blocking viral entry and replication.
After three days of treatment, children who received ziresovir demonstrated greater clinical improvement, with a mean reduction of 3.5 points in the Wang score compared to 2.2 points in the placebo group. Improvements were consistent across all score components, including respiratory muscle retraction, respiratory rate, and wheezing. Ziresovir treatment was also associated with a significant reduction in viral load. The authors note that future research should include larger cohorts and direct comparisons with other antivirals such as ribavirin.