For the first time there are safe and effective RSV prevention treatments

Respiratory syncytial virus (RSV) is the number one cause of hospitalization in infants, accounting for about 25% of all their hospitalizations. However, a study published in Morbidity and Mortality Weekly Report shows that for the first time we have very effective and safe strategies that can reduce at least by 50% all RSV-related hospitalizations in young infants, the most vulnerable age group.

Researchers at Baylor College of Medicine and Texas Children’s Hospital through their participation in the New Vaccine Surveillance Network (NVSN) played a leading role in this multi-institutional study conducted by the U.S. Centers for Disease Control and Prevention (CDC).

“RSV is a common respiratory virus that causes infections of the lungs and upper respiratory tract. Symptoms can range from mild cold-like illness to severe respiratory disease such as bronchiolitis and pneumonia, requiring hospitalization,” said Baylor co-investigator Dr. Flor M. Muñoz, associate professor of pediatrics - infectious disease at Baylor and Texas Children’s Hospital. “RSV can affect people of all ages, but it is particularly dangerous for infants and young children. Infants aged 0-3 months are at the highest risk for severe RSV disease.”

In recent years, two preventive treatments were developed to reduce the severity of RSV infection: a maternal RSV vaccine to protect infants during their first six months of life through the passage of maternal antibodies to the infant, and a long-acting monoclonal antibody directly administered to all infants aged 0 to 7 months of age to protect during their first RSV season. 

“These treatments became available for prevention of severe RSV disease among infants during the 2023-2024 and the 2024–25 RSV seasons. In this study, we evaluated the effectiveness of the treatments in reducing the risk of hospitalization in nearly 20,000 infants in the U.S. population during the study period,” said Baylor co-investigator Dr. Pedro A. Piedra professor of molecular virology and microbiology, pediatrics, and pharmacology and chemical biology at Baylor. 

The researchers compared the rates of hospitalizations of children younger than 5 years for the 2024–25 and 2018–20 RSV seasons using data from the RSV-Associated Hospitalization Surveillance Network (RSV-NET) and the NVSN. 

Infants in the study were protected either by vaccinating their mothers during pregnancy with the maternal RSV vaccine or by receiving at birth a dose of long-acting monoclonal antibodies against the virus. 

“This long-awaited study is important because for the first time we are able to see the impact these prevention strategies for RSV have in real life, in the United States,” Muñoz said. “We were excited to find that implementing both prevention measures improved coverage and significantly reduced RSV-associated hospitalizations among infants aged 0-7 months during the 2024-25 season compared to the 2018-20 seasons.”

“We found the greatest impact on the youngest infants, 0 to 2 months old, the ones at the highest risk for severe RSV disease,” Piedra said. “We can now reduce at least 50% of all RSV-related hospitalizations in the most vulnerable age group.”

“We also learned about the importance of timely administration of these prevention measures,” said Baylor co-investigator Dr. Vasanthi Avadhanula, assistant professor of molecular virology and microbiology at Baylor. “The reduction in hospitalizations was most pronounced during the peak RSV season, which is from December to February for most locations. However, in Houston and other Texas cities and Southern states, the RSV season starts much earlier. In South Florida, RSV may circulate throughout the year.”

In Houston, the interventions were implemented later into its RSV season, so they did not have the same impact as in other cities where the implementation occurred before the RSV season started. “Having epidemiological data showing when the virus is present in the population is important because it helps to decide when to implement these interventions in a timely manner to increase their benefits to the infant population,” Avadhanula said.

The findings from this study have significant implications for public health practices. 

“For these RSV protection measures to be effective it’s crucial to follow the recommendations for administering the maternal RSV vaccine during pregnancy and the long-acting RSV monoclonal antibody to infants within the first week of life, as early as possible in the RSV season,” Piedra said. 

“There are still many infants who are not benefiting from this protective measures. Increasing the coverage can lead to even greater reductions in RSV-associated hospitalizations,” Muñoz said. “While infants who receive these treatments might still get infected with this very common virus, the risk of having severe disease that would require hospitalization will be reduced significantly. Public health efforts should therefore focus on educating healthcare providers and parents about the benefits of these measures to increase coverage.”

“In addition, ongoing monitoring and evaluation of RSV hospitalization rates are essential to understand the long-term impact of these prevention strategies and to make necessary adjustments in public health recommendations,” Avadhanula said. 

As we continue to navigate the RSV season, ensuring that these products are widely available and administered in a timely manner will be key to protecting our youngest and most vulnerable populations.

The New Vaccine Surveillance Network funded by the CDC is the only network in the U.S. that generates enhanced surveillance for multiple disease-causing agents to assess pediatric viral respiratory and gastrointestinal infections and vaccine impact in children 0 up to 18 years of age. “I consider NVSN one of the jewels of the infectious agents surveillance systems in the U.S.,” Piedra said. 

Dr. Julie Boom is the principal investigator of the NVSN at Texas Children’s Hospital and Baylor College of Medicine. For a complete list of the contributors to this work and their affiliations, see the publication.