Beyfortus Shows Stronger Public Health Impact Than Maternal RSV Vaccine in Landmark Real-World Comparison
In a pivotal step forward for infant respiratory health, new real-world data from an immunization program in Spain reveal that Beyfortus® (nirsevimab), a long-acting monoclonal antibody developed by Sanofi and AstraZeneca, significantly reduced hospitalizations due to respiratory syncytial virus (RSV) among infants. According to findings presented at the 43rd Annual Meeting of the European Society for Paediatric Infectious Diseases (ESPID), held in Bucharest, Romania, the Spanish public health program that implemented Beyfortus achieved a 69.0% reduction in RSV-related infant hospitalizations during the 2024–2025 RSV season compared to the 2022–2023 season.
This landmark real-world analysis not only reinforces Beyfortus’ clinical efficacy but also serves as the first international comparative evaluation of public health strategies for preventing RSV in infants. In contrast to the results from Spain, a similar national program in the United Kingdom, which relied solely on maternal immunization using Pfizer’s RSVpreF vaccine (Abrysvo), showed a 26.7% reduction in RSV-related hospitalizations among infants over the same two RSV seasons. The significant difference in outcomes provides important insights for health policymakers and pediatric health experts weighing strategies for RSV prevention.
These data are part of Sanofi’s REACH study (Retrospective Evaluation Assessing Country-level impact of nirsevimab on Hospitalizations), a large-scale, multi-country, retrospective observational study that examines the public health impact of RSV immunization programs across Europe. The late-breaking data were presented in an oral session titled “Session 09: Late Breaking,” held on May 30, 2025, during the ESPID meeting, which runs from May 26 to May 30.
The REACH of Real-World Evidence
The REACH study marks the first time researchers have compared RSV immunization strategies on a country-wide scale, using real-world evidence to evaluate the relative effectiveness of two distinct approaches: direct infant immunization with a long-acting monoclonal antibody (Beyfortus) versus maternal vaccination during pregnancy.
Spain’s national program, launched ahead of the 2024–2025 RSV season, provided Beyfortus to all infants, regardless of gestational age or health status. This universal approach mirrored clinical guidance suggesting that RSV poses a threat to all infants—not just those born prematurely or with underlying conditions.
In the UK, by contrast, the RSVpreF maternal vaccine was offered to pregnant women during the third trimester with the goal of conferring passive immunity to newborns. While this method demonstrated some public health benefit, it was notably less effective than the direct immunization strategy used in Spain.
The sharp contrast in hospitalization outcomes—69.0% reduction with Beyfortus versus 26.7% with RSVpreF—underscores the practical advantages of direct infant immunization in reducing RSV disease burden. Experts at ESPID noted that while maternal immunization has value, its impact may be limited by timing constraints and reduced antibody transfer efficiency, especially among preterm infants or those born before RSV season onset.
Reinforcing Clinical Findings with HARMONIE
The real-world findings presented in the REACH study were bolstered by additional data from the HARMONIE Phase 3b clinical study, also presented at ESPID and recently published in The Lancet Child & Adolescent Health. The new data extend the duration of follow-up to 180 days, showing that Beyfortus continues to offer robust protection throughout and beyond the typical five-month RSV season.
In this updated analysis, Beyfortus reduced RSV-related hospitalizations by 82.7% (95% Confidence Interval: 67.8 to 91.5; p<0.0001) over a six-month period compared to no RSV intervention. These results not only confirm but slightly improve upon the earlier-reported primary analysis, which demonstrated 83.2% efficacy. Importantly, the efficacy remained consistent across infants born before or during the RSV season, with no evidence of waning protection.
This long duration of protection is particularly significant, given that nearly half of RSV hospitalizations in infants occur among those born before the RSV season begins. For these infants, maternal vaccination may offer insufficient antibody levels to last through the entire season, whereas direct infant immunization with a long-acting monoclonal antibody like Beyfortus ensures sustained protection when it’s most needed.
Speaking on the new findings, Thomas Triomphe, Executive Vice President of Vaccines at Sanofi, emphasized the public health implications of the data.
“The six-month data from HARMONIE show Beyfortus’ protection exceeded the typical five-month RSV season,” Triomphe stated. “This is important because half of infant RSV hospitalizations occur in older babies born before the RSV season begins. These data demonstrating high, sustained efficacy, combined with real-world public health impact data, underscore how Beyfortus provides proven protection against the number one cause of lower respiratory tract disease in all infants.”
Cost-Effectiveness and Policy Implications
In addition to efficacy, cost-effectiveness remains a key driver for national immunization policies. New data presented at ESPID (Poster #EV1006) demonstrate that Beyfortus not only prevents more medically attended RSV cases than clesrovimab—another long-acting monoclonal antibody under development—but also offers superior value for public health systems.
Beyfortus was shown to be cost-effective across a range of healthcare settings, supporting its broader adoption in public immunization programs. Its ability to prevent a higher volume of doctor visits, emergency room visits, and hospital admissions translates into substantial savings for healthcare systems while simultaneously reducing parental stress and burden.
A Growing Body of Global Evidence
The strength of Beyfortus’ profile is also supported by an expanding base of real-world data. To date, more than 40 studies conducted across four continents have evaluated its safety, effectiveness, and implementation feasibility. These studies have collectively involved more than 250,000 immunized infants—making it the most extensively studied RSV prevention intervention for infants to date.
Furthermore, over six million infants worldwide have now received Beyfortus since its introduction, reflecting widespread acceptance among both healthcare providers and parents. This global reach enhances the generalizability of study results and builds confidence in the product’s consistent performance across different populations, healthcare systems, and epidemiological settings.
With the 2025–2026 RSV season on the horizon, the implications of these findings are likely to shape immunization policies worldwide. Countries currently evaluating or piloting maternal RSV immunization strategies may need to reconsider their approach in light of the stronger impact observed with direct infant immunization programs.
For Sanofi and AstraZeneca, the developers of Beyfortus, the convergence of clinical trial and real-world evidence presents a compelling case for broader adoption. As more countries evaluate cost-benefit scenarios, the preference may tilt increasingly toward monoclonal antibody-based infant immunization—particularly for maximizing public health benefit.
In summary, the REACH and HARMONIE studies together offer a comprehensive, data-driven affirmation of Beyfortus’ potential to redefine RSV prevention in infants. Its proven ability to deliver high, sustained protection with a strong safety profile, combined with robust real-world effectiveness and favorable cost-effectiveness metrics, positions it as a cornerstone of future pediatric respiratory health strategies.
