Blame my dad for my love of ’60s and ’70s rock bands: The phrase “the kids are alright” came to mind when I read the recent study out of Spain looking at the impact of universal nirsevimab prophylaxis.
Infants younger than 6 months carry the overwhelming burden of respiratory syncytial virus. In 2023, RSVpreF vaccine (Abrysvo) was approved for use in patients between 32 and 37 weeks pregnant who would deliver between September and January (this is a one-time vaccine). That same year, nirsevimab (Beyfortus) – a monoclonal antibody infusion – was approved for infants born to an unvaccinated parent between the months of October and March. In 2025, clesrovimab (Enflonsia), another monoclonal antibody, was also approved.
An area in northwest Spain was home to early adopters of nirsevimab, where a universal RSV prophylaxis policy was implemented as part of the area’s immunization program (they studied these infants through the NIRSE-GAL protocol). Multiple studies have shown the efficacy of nirsevimab as it relates to reduced rates of RSV-related hospitalization, ICU admission and lower respiratory tract infection. The NIRSE-GAL authors found similar findings. They then set out to look at alternative outcomes, which were published in Lancet Infectious Diseases.
They looked at real-world data for 18 months of follow up after implementing universal nirsevimab prophylaxis in 2023-2024. The primary endpoint was RSV-related LRTI hospitalization. Secondary endpoints included first occurrence and first recurrence of LRTI hospitalization, acute bronchitis or bronchiolitis hospitalization, or pneumonia hospitalization from any cause; all-cause hospitalization; and first recurrence of RSV-related LRTI hospitalization. Additional secondary endpoints included first and second visits for acute bronchitis or bronchiolitis, wheezing or asthma, LRTI, respiratory infections, acute otitis media and all-otitis diagnosis.
The study looked at 14,476 eligible infants: 12,492 were included in the study, and 11,796 (94.4%) were immunized (48.7% female). First-time RSV-related hospitalization rates were reduced by 85.9% in the first RSV season and 55.3% in the second. First-time hospitalization for LRTI from any cause was reduced by 59.8% in the first RSV season. The number needed to immunize to prevent one hospitalization was 34. First-time bronchitis or bronchiolitis admissions decreased by 59.0% (NNI = 49), and first recurrence decreased by 75.9% (the reduction was sustained through the second RSV season). First-time pneumonia hospitalizations decreased by 53.1%; all first all-cause hospitalizations decreased by 20.3%; and recurrent all-cause hospitalizations fell by 29%.
In the outpatient setting, nirsevimab was associated with a reduction of nearly one-third in first primary care visits for LRTI, acute bronchitis or bronchiolitis, and wheezing or asthma. There was no change in visits for otitis.
While the reductions in pulmonary-related events and hospitalizations are not surprising, the fact that all-cause hospitalization was reduced was a little surprising. The authors speculate that this reduction is likely due to the high burden of RSV-related hospitalizations in infants rather than any other protective effects.
In the last two years, the immunization landscape has changed dramatically, with some questioning the efficacy and utility of various immunizations, especially in the very young. This real-world study shows nirsevimab’s broad impact on infant morbidity. Hopefully, parents will be open to hearing this good news.
