image: The PAS Meeting connects thousands of leading pediatric researchers, clinicians, and educators worldwide, united by a shared mission: connecting the global academic pediatric community to advance scientific discovery and promote innovation in child and adolescent health.
Credit: Pediatric Academic Societies
BOSTON, April 24, 2026 – A new study found that infants receiving maternal Respiratory Syncytial Virus (RSV) vaccination or Nirsevimab after birth had significantly lower RSV infection and healthcare use compared to unprotected infants. It also showed fewer severe complications in RSV-positive infants with prevention. These findings highlight the positive impact of RSV preventative measures in high-risk populations. Findings from the study will be presented at the Pediatric Academic Societies (PAS) 2026 Meeting, taking place April 24-27 in Boston.
RSV is a leading cause of respiratory infections and hospitalization in infants under 6 months in the United States. In 2023, the U.S. Food and Drug Administration approved two new preventive immunizations against RSV to protect infants: Pfizer’s Abrysvo, a maternal vaccine administered between 32 and 36 weeks of pregnancy, and Sanofi’s Nirsevimab (Beyfortus), a long-acting monoclonal antibody injection. Real-world data on their effectiveness remain limited, especially in high-risk and underserved groups. During October 2023, New York faced a “tripledemic” of RSV, influenza and COVID-19. Researchers analyzed hospitalizations, respiratory support, and 180-day outcomes following RSV infection, along with other circulating respiratory viruses.
“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, principal investigator and senior author of the study. “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. 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 healthcare 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!’”
Additional information is included in the below research abstract. The PAS Meeting connects thousands of leading pediatric researchers, clinicians and educators worldwide. View the full schedule in the PAS 2026 program guide. For more information about the PAS Meeting, please visit www.pas-meeting.org.
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About the Pediatric Academic Societies (PAS) Meeting
The Pediatric Academic Societies (PAS) Meeting connects thousands of leading pediatric researchers, clinicians, and educators worldwide, united by a shared mission: connecting the global academic pediatric community to advance scientific discovery and promote innovation in child and adolescent health. PAS is a partnership of four premier pediatric associations: the American Academy of Pediatrics (AAP), the Academic Pediatric Association (APA), the American Pediatric Society (APS), and the Society for Pediatric Research (SPR). For more information, visit www.pas-meeting.org. Follow us on X, Facebook, and Instagram.
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Abstract: Effectiveness of Maternal RSV Vaccination and Nirsevimab in Preventing and Reducing Severity of RSV-Related Illness in Infants Under 6 Months
Presenting Author
Helly Thakkar, MD, MPH, Resident, Icahn School of Medicine at Mount Sinai
Organization
Icahn School of Medicine at Mount Sinai
Topic
Neonatal General
Background
Respiratory Syncytial Virus (RSV) is a leading cause of respiratory illness and hospitalization in infants under six months. In 2023, the U.S. FDA approved two new preventives: Pfizer’s Abrysvo, a maternal vaccine given at 32–36 weeks’ gestation, and Nirsevimab (Beyfortus), a monoclonal antibody for infants. Real-world data on their effectiveness remain limited, especially in high-risk and underserved groups. During October 2023, New York faced a “tripledemic” of RSV, influenza, and COVID-19. We analyzed hospitalizations, respiratory support, and 180-day outcomes following RSV infection, along with other circulating respiratory viruses.
Objective
To assess the effectiveness of Abrysvo and Nirsevimab in preventing RSV infection and severity in infants under six months at a New York City hospital by comparing hospitalization rates, respiratory support needs, and RSV burden within the first 180 days.
Design/Methods
A retrospective study at NYC Health + Hospitals / Elmhurst reviewed records of 1,259 infants born between October 2023 and March 2024. Infants were grouped by RSV prevention: 861 with maternal Abrysvo, 115 with Nirsevimab before discharge, and 277 with no prevention; six received both. Primary outcomes measured RSV infection and severity within 180 days, including hospitalization and oxygen use. Secondary outcomes involved illnesses from COVID-19, influenza, and other viruses. Analyses used Chi-square tests and effect size measures like Phi and Cramer’s V.
Results
Among 1,259 infants, 37 (2.9%) tested positive for RSV. RSV infection rates were 1.7% in the Abrysvo group, 0% in the Nirsevimab group, and 7.9% in the no-prevention group (χ²=123.72, p< 0.0001, Cramer’s V=0.22). Among RSV-positive infants, hospitalization was lower with prevention (1/15, 6.7%) than without (9/22, 40.9%) (p=0.0213). Oxygen was needed in 0% of prevention infants versus 27.3% in no-prevention (p=0.0271). Emergency visits showed no difference (p=0.24), but outpatient visits were higher in the prevention group (40% vs. 9.1%, p=0.0249). During the period, 44 COVID-19 and 31 flu cases occurred, with no RSV co-infections.
Conclusion(s)
Our study found that infants receiving maternal RSV vaccination or Nirsevimab after birth had significantly lower RSV infection and healthcare use compared to unprotected infants. It also showed fewer severe complications in RSV-positive infants with prevention. These findings highlight the positive impact of RSV preventative measures in high-risk populations.
Co-Authors
Uday P. Patil, MD, Associate Professor of Pediatrics & Global Health, Icahn School of Medicine at Mt. Sinai-NYC H+H/ Elmhurst
Bharti Sharma, MD, Icahn School of Medicine at Mount Sinai
Chaithanya Avanthika, MD, Icahn School of Medicine at Mount Sinai
Tables and Images
Health care utilization in RSV positive patients
Histogram showing total number of patients in different sub groups
Forrest plot measuring effect size of RSV prevention with respect to O2 requirement, hospitalization and RSV infection