Two new studies examining prevention strategies for respiratory syncytial virus (RSV) suggest that both maternal vaccination and infant immunization reduce RSV-associated hospitalizations, with the long-acting monoclonal antibody nirsevimab tied to greater protection against severe disease.

In a nationwide population-based cohort study from France published in JAMA, researchers compared maternal vaccination with the RSVpreF vaccine (Abrysvo) during late pregnancy with passive infant immunization using nirsevimab (Beyfortus). The study included more than 42,000 infants born between September and December 2024 and followed them through February 2025.

Overall, infants who received nirsevimab had a significantly lower risk of RSV-related hospitalization than those protected through maternal vaccination alone. Among 481 RSV-associated hospitalizations, 44% occurred in the nirsevimab group, compared with 56% in the maternal vaccine group (between-group difference, -11.8%). 

Infants who received nirsevimab had substantially lower risks of pediatric intensive care unit admission (adjusted hazard ratio [aHR], 0.58), ventilator support(aHR, 0.57), and oxygen therapy (adjusted HR, 0.56).

“Compared with maternal vaccination with the RSVpreF vaccine, passive infant immunization with nirsevimab was associated with lower risks of RSV-related hospitalization and severe outcomes,” the authors wrote, noting that the findings reflect the first RSV season in France in which both products were used.

Nirsevimab 81% effective against RSV hospitalization 

Complementary findings from the United States were published on the same day in JAMA Pediatrics. 

The population-based surveillance study assessed the effectiveness of both RSV prevention strategies among 5,029 children younger than 2 years with medically attended acute respiratory infection (ARI) during the 2024-25 season. 

Using a test-negative case-control design across seven pediatric medical centers, a Centers for Disease Control and Prevention–led research team estimated nirsevimab effectiveness among infants at 81% against RSV-associated hospitalization; it remained at 77% for 130 to 210 days after vaccination. Maternal vaccine effectiveness was 64% against medically attended ARI and 70% against hospitalization 

Overall, hospitalization rates were reduced by an estimated 41% to 51% among infants aged 11 months or younger, compared with 2017-20 rates. The highest reduction (56% to 63%) occurred in newborns aged 0 to 2 months.

“Both maternal RSV vaccine and nirsevimab were estimated to be effective at protecting infants from RSV-associated hospitalizations in their first RSV season,” note the authors. “RSV-associated hospitalization rates in newborns and infants aged 0 to 11 months were reduced by up to half compared to seasons before these products were introduced.”