Every winter, hospitals around the world fill with infants struggling to breathe because of respiratory syncytial virus (RSV). Estimates show that RSV infects nearly every child by the time they turn two, and it is a leading cause of hospitalisation for lower respiratory tract infections in infants. Despite this huge burden, no antiviral treatment has yet been approved for young children with RSV.
The Penta-sponsored THAI-CARES RSV study was launched in 2025 to start closing this gap, testing whether remdesivir, an antiviral already used in children with COVID-19, could also help babies and toddlers hospitalised with RSV-associated lower respiratory tract infections.
Between July and September 2025, the study enrolled 120 children under two years old in eight hospitals in Thailand. Now, preliminary results presented at ESPID in June 2026 offer the first answers.
The first and most important question the study set out to answer is whether remdesivir is safe for this very young age group. Half of the children received standard hospital care alone (oxygen, fluids and other supportive treatments as needed), while the other half received the same care plus a five-day course of intravenous remdesivir. The results here are reassuring: remdesivir was well tolerated, with no drug-related side effects identified and no child needing to stop treatment early.
On the question of how well the drug fights the virus itself, the picture was more mixed. By Day 6, viral levels in the nose and upper throat had dropped at a similar rate whether or not children received remdesivir. However, children who received remdesivir tended to have less severe respiratory illness symptoms by Day 6, according to a standardised respiratory severity score – although the difference was not statistically significant.
Two findings stood out as particularly promising and will guide future research. First, children who started remdesivir within three days of their symptoms beginning seemed to recover with notably less respiratory distress than those on standard care alone. Second, infants under six months old, often the most vulnerable to severe RSV, also seemed to benefit more from the treatment.
Both of these observations come from smaller subgroups of the study and are exploratory, so they will need to be confirmed in larger studies. But they offer a roadmap: timing matters, and the very youngest infants may be the ones to watch most closely in future research.
This study is the first randomised controlled study on remdesivir specifically designed for infants and young children hospitalised with lower respiratory tract infections. While it does not yet provide definitive evidence that remdesivir improves outcomes, there are no safety concerns in this age group and it establishes that the drug can be used for specific situations, namely early treatment and very young infants, where the benefit might be greatest.
View slides presented at ESPID 2026
The THAI-CARES RSV study is conducted across eight sites in Thailand, sponsored by Fondazione Penta ETS, and supported with funding and provision of remdesivir by Gilead Sciences, Inc. (CO-US-540-7443).