Sanofi's Beyfortus has demonstrated superior real-world effectiveness in preventing infant respiratory syncytial virus (RSV) hospitalizations compared to maternal vaccination strategies, according to groundbreaking data presented at the 43rd Annual Meeting of the European Society for Paediatric Infectious Diseases (ESPID) in Bucharest, Romania.
Comparative Real-World Effectiveness
The observational REACH study revealed striking differences between infant and maternal RSV immunization approaches. Spain's Beyfortus-only immunization program targeting all infants reduced RSV hospitalizations by 69.0% during the 2024-2025 RSV season compared to the 2022-2023 baseline season. In contrast, the UK's RSVpreF-only maternal vaccination program achieved a 26.7% reduction in infant RSV hospitalizations over the same period.
This marks the first multi-country public health impact analysis comparing different infant RSV prevention programs, providing crucial evidence for healthcare policymakers worldwide. The REACH study utilized administrative and microbiology data from multiple hospital sites across Spain and the UK, analyzing three consecutive RSV seasons from June 2022 through March 2025.
Extended Protection Duration
New durability data from the HARMONIE Phase 3b clinical study, published in The Lancet Child & Adolescent Health, demonstrate that Beyfortus reduced RSV hospitalizations by 82.7% (95% CI: 67.8 to 91.5; p<0.0001) through six months compared to no intervention. This protection period exceeds the typical five-month RSV season, addressing a critical clinical need.
"The six-month data from HARMONIE show Beyfortus' protection exceeded the typical five-month RSV season," said Thomas Triomphe, Executive Vice President of Vaccines at Sanofi. "This is important because half of infant RSV hospitalizations occur in older babies born before the RSV season begins."
The sustained efficacy of 83.2% previously reported in the primary analysis showed no evidence of waning protection in infants born before or during the RSV season. Beyfortus maintained a favorable safety profile consistent with clinical study results throughout the extended follow-up period.
Clinical Trial Design and Population
The HARMONIE study enrolled more than 8,000 infants born with a gestational age of 29 weeks or greater during the 2022-2023 RSV season across nearly 250 sites. The Phase 3b trial was conducted under multi-country, close to real-world conditions to evaluate efficacy and safety in infants up to 12 months of age who were not eligible to receive palivizumab.
Primary results published in The New England Journal of Medicine confirmed 83.2% efficacy (95% CI 67.8 to 92.0; P<0.001) against RSV-related hospitalizations and 75.7% efficacy (95% CI: 32.8 to 92.9; P=0.004) against very severe RSV lower respiratory tract disease compared to standard of care.
Global Disease Burden and Economic Impact
RSV represents a significant global health challenge, with two out of three infants infected during their first year of life and nearly all children infected by their second birthday. The virus is the most common cause of lower respiratory tract disease, including bronchiolitis and pneumonia, in infants.
Globally, approximately 33 million cases of acute lower respiratory infections occurred in 2019, leading to more than three million hospitalizations in children younger than five years. RSV-related direct medical costs, including hospital, outpatient and follow-up care, were estimated at approximately €5 billion in 2017.
Comprehensive Real-World Evidence
Beyfortus has accumulated real-world data from over 40 studies spanning four continents and more than 250,000 immunized infants, representing the largest body of public health impact data for infant RSV protection. With more than six million infants immunized globally, the treatment has demonstrated consistent acceptance among parents and healthcare providers.
Additional cost-effectiveness data presented at ESPID 2025 showed Beyfortus prevents more medically attended RSV cases compared to clesrovimab, another antibody in development, reinforcing its economic value in preventing RSV disease.
Mechanism and Administration
As a long-acting antibody administered directly to newborns and infants as a single dose, Beyfortus provides rapid and direct protection against RSV-induced lower respiratory tract disease without requiring immune system activation. The treatment is designed for all infants, including those born before or during the RSV season, healthy term or preterm infants, and those with specific health conditions.
Beyfortus has received regulatory approval in the United States, European Union, China, Japan, and numerous other countries worldwide. The treatment received special designations including breakthrough therapy designation and fast track designation in the US, PRIority MEdicines (PRIME) and accelerated assessment in the EU, and similar priority designations in Japan and China.
