A new study from Spain shows that giving all infants a long-acting antibody called nirsevimab slashed hospitalizations for respiratory syncytial virus by 86% — one of the most striking results yet for a tool many pediatric health experts have been waiting years to see in action. The findings, published in the European Journal of Pediatrics on May 16, 2025 C.E., add powerful real-world evidence to a growing case for universal infant immunization against RSV.
At a glance
- Nirsevimab prophylaxis: All infants in the study’s catchment area received the long-acting monoclonal antibody before or during RSV season, making this a true population-level intervention rather than a targeted program.
- Hospitalization reduction: RSV-associated lower respiratory tract infections sent 86% fewer infants to the hospital compared to previous seasons, with pediatric intensive care admissions falling sharply as well.
- Youngest infants: Babies under 6 months old — historically the most vulnerable to severe RSV — saw the greatest benefit from the intervention.
Why RSV has been so hard to fight
Respiratory syncytial virus is the leading cause of hospitalization in infants worldwide. Nearly all children catch it before their second birthday, but for those under six months, it can mean days on oxygen or in intensive care. For decades, the only preventive option was palivizumab, a costly antibody treatment approved only for high-risk infants. Most healthy babies had no protection at all.
Nirsevimab changed that equation when regulators in Europe and the U.S. approved it for universal infant use. Unlike a traditional vaccine, it delivers ready-made antibodies directly — no immune response required, which matters enormously for newborns whose immune systems are still developing. The question was whether it would perform as well in the real world as it had in clinical trials.
What the Spanish researchers found
The team at Valladolid University’s Faculty of Medicine, led by Lorena Bermúdez-Barrezueta, tracked hospitalizations and pediatric intensive care unit admissions at a single center in Valladolid, Spain, before and after the rollout of a universal nirsevimab program. The contrast was stark.
Hospitalizations for RSV-associated lower respiratory tract infections fell by 86%. Pediatric intensive care admissions dropped as well. The effect was concentrated most heavily in infants under six months — the cohort that fills hospital wards every winter and strains pediatric services across the Northern Hemisphere.
“These findings are encouraging, and it is anticipated that in the coming years, nirsevimab prophylaxis will mitigate the significant burden on healthcare services during the winter season,” the authors wrote. The study was supported by FEDER European Funds, the Junta de Castilla y León, and the Ernesto Sanchez Villares Foundation.
The bigger picture for global infant health
RSV hospitalizations are not evenly distributed. Low- and middle-income countries carry a disproportionate share of severe cases and deaths, and nirsevimab remains expensive and out of reach for most of the world’s families. Spain’s results are encouraging precisely because they show what universal coverage can do — but they also highlight how far access still needs to travel.
Several countries in Europe have now begun national nirsevimab programs, and the European Medicines Agency approved the antibody for all infants in 2022 C.E. In the U.S., the Centers for Disease Control and Prevention added nirsevimab to its infant immunization schedule for the 2023–2024 C.E. season. Early U.S. data, published by the CDC’s Morbidity and Mortality Weekly Report, also showed substantial drops in RSV hospitalizations among immunized infants — lending further weight to the Spanish findings.
Researchers and advocates are now watching whether programs like Spain’s can inform World Health Organization guidance and accelerate access negotiations in lower-income settings. The gap between what is possible and what is available to most families remains real and urgent.
A cautious but genuine reason for hope
Single-center studies have real limits. Valladolid’s experience reflects one hospital system, one region, and one winter season — and the relatively small sample size means results should be interpreted alongside the broader body of evidence rather than in isolation. Longer follow-up across multiple sites and seasons will be needed to confirm the durability of these effects and to understand how well the antibody performs as RSV strains evolve.
Still, the direction of the evidence is consistent. A preventable disease that has filled pediatric wards for generations may be genuinely on the retreat — at least in places with the resources to act. The work now is making sure that circle widens.
Read more
For more on this story, see: Medscape
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