Maternal RSV vaccination and nirsevimab reduce infection, severity in infants younger than 6 months

Maternal respiratory syncytial virus (RSV) vaccination and postnatal administration of nirsevimab were associated with reduced infection rates and disease severity among infants younger than 6 months, according to new data presented at the 2026 Pediatric Academic Societies (PAS) Meeting.^1,2

The findings, derived from a retrospective study conducted at NYC Health + Hospitals/Elmhurst, provide early real-world evidence on the effectiveness of 2 recently approved RSV preventive strategies: Pfizer’s Abrysvo, administered during pregnancy, and Sanofi’s nirsevimab (Beyfortus), a long-acting monoclonal antibody given to infants.

RSV remains a leading cause of respiratory illness and hospitalization in young infants, particularly those younger than 6 months. The introduction of these preventive options in 2023 marked a significant shift in pediatric infectious disease prevention, although data in diverse and underserved populations have been limited.

“The disease burden of RSV in this young infant population is tremendous, leading to about half a million emergency room visits and over 100,000 hospital admissions every year,” said Uday Patil, MD, FAAP, associate chair of pediatrics at NYC Health + Hospitals/Elmhurst and senior author of the study.

Study design evaluates outcomes during first RSV season of new immunizations

The study, presented at the 2026 PAS Meeting, evaluated 1,259 infants born between October 2023 and March 2024, a period that coincided with a “tripledemic” of RSV, influenza, and COVID-19 in New York. Investigators categorized infants based on RSV prevention exposure: 861 received maternal vaccination with Abrysvo, 115 received nirsevimab prior to hospital discharge, 277 received no preventive intervention, and 6 received both.

The primary outcomes included RSV infection and severity within the first 180 days of life, measured by hospitalization and need for respiratory support. Secondary outcomes included infections from other circulating respiratory viruses.

Lower RSV infection rates observed with maternal vaccination and nirsevimab

Overall, 37 infants (2.9%) tested positive for RSV. Infection rates differed significantly by prevention status. Infants whose mothers received Abrysvo had an RSV infection rate of 1.7%, while no infections were observed among infants who received nirsevimab. In contrast, infants without preventive measures had a markedly higher infection rate of 7.9% (P < .0001).

Among infants who developed RSV infection, those with preventive exposure experienced less severe disease. Hospitalization occurred in 6.7% of infants in the prevention group compared with 40.9% of those without prevention (P = .0213). Similarly, none of the infants in the prevention group required supplemental oxygen, whereas 27.3% of unprotected infants did (P = .0271).

Emergency department utilization did not differ significantly between groups; however, outpatient visits were more frequent among infants who received preventive measures. Investigators noted that this may reflect increased health care engagement among families who accepted vaccination or immunization.

High uptake in underserved population highlights feasibility

“Our study investigated the impact of these immunizations during their very first season after they became available on preventing RSV infection–related morbidities in infants under 6 months old in one of the most diverse and medically underserved neighborhoods in Queens, New York City, served by Elmhurst Hospital,” Patil said. “We found a high uptake (>65%) of the maternal RSV vaccine (Abrysvo) among our pregnant patients and of infant immunization (Beyfortus) among newborns (>90%). This indicates strong patient confidence in the health care system within our vulnerable population. The rates of RSV infections, hospitalizations, and severity of illness all declined significantly among infants in our study, demonstrating the high effectiveness of both of these immunizations. Our findings yield pragmatic results, emphasizing that these new preventive strategies against RSV are game-changers and confirming the saying that ‘an ounce of prevention is worth a pound!’”

No cases of RSV coinfection with COVID-19 or influenza were identified during the study period, although 44 COVID-19 cases and 31 influenza cases were reported.

Findings support broader adoption of RSV preventive measures

These findings suggest that both maternal RSV vaccination and infant immunization with nirsevimab can reduce not only the incidence of RSV infection but also the severity of illness among affected infants. The data also support the feasibility and uptake of these interventions in a high-risk, underserved urban population.

As RSV prevention strategies expand, these real-world results may inform clinical decision-making and public health efforts aimed at reducing RSV-related morbidity in early infancy.

References

1. New study examines effectiveness of maternal RSV vaccination and nirsevimab in preventing and reducing severity of RSV-related illness in infants. Pediatric Academic Societies. News release. April 24, 2026. Accessed April 24, 2026. https://www.eurekalert.org/news-releases/1125635

2. Thakkar H, Patil UP, Sharma B, Avanthika C. Effectiveness of maternal RSV vaccination and nirsevimab in preventing and reducing severity of RSV-related illness in infants under 6 months. Presented at: 2026 PAS Meeting; April 24-27, 2026; Boston, MA.