87% reduction in cases of respiratory syncytial virus (RSV) disease across all sites of care among healthy, term babies, born ahead of or during the RSV season
98% reduction in hospitalizations of babies with RSV compared to those who did not get BEYFORTUS, per new post-hoc analysis
MORRISTOWN, N.J., July 22, 2025 /PRNewswire/ -- The largest US real-world study of BEYFORTUS (nirsevimab-alip) 50mg and 100mg Injection successfully met both of its co-primary endpoints, demonstrating that BEYFORTUS provides protection for babies against RSV disease. The full results from the "Effectiveness of nirsevimab against RSV and RSV-related events in infants" study have been published in PEDIATRICS®, an official journal of the American Academy of Pediatrics.
The study, conducted during the 2023-2024 RSV season, further supports the broad use of BEYFORTUS as a proven RSV prevention designed to protect all infants, including those born healthy or with underlying conditions, full term or preterm, before or during the RSV season. BEYFORTUS is a long-acting monoclonal antibody approved for the prevention of RSV lower respiratory tract disease (LRTD) in newborns and infants born during or entering their first RSV season, and for children up to 24 months of age who remain vulnerable to severe RSV disease through their second RSV season.
Ayman Chit
Head of North America Medical, Vaccines, Sanofi
"These results support BEYFORTUS as a groundbreaking advancement in infant RSV disease prevention. With more than 40 real-world evidence studies to date, this latest study further strengthens the well-established body of data that shows that BEYFORTUS provides protection against RSV disease to help safeguard the health of all babies, regardless of whether they are born before or during the RSV season."
The first co-primary endpoint showed babies administered BEYFORTUS were 87% (CI: 81.7%-91.1%; p<0.0001) less likely to develop RSV disease compared to babies who did not receive BEYFORTUS. The second co-primary endpoint showed that if a baby who received BEYFORTUS later tested positive for RSV lung infection there were fewer overall medical visits (adjusted mean difference -0.86, p=0.001) during the illness, including significantly reduced visits to emergency departments and hospitalizations.
Additionally, a post hoc analysis of the study evaluated the effectiveness of BEYFORTUS in preventing RSV hospitalizations among healthy term babies. Using real-world data from a retrospective cohort design, researchers compared hospitalization rates between babies who received BEYFORTUS and those who did not. The analysis demonstrated a 98% reduction in RSV hospitalizations among babies given BEYFORTUS compared to those who were not.
The study was a large, real-world, retrospective cohort analysis that included more than 30,000 healthy, full-term babies who were eligible to receive BEYFORTUS. The study excluded babies at high risk for severe RSV disease such as those with underlying medical conditions or those born preterm, allowing for a clear evaluation of the impact of BEYFORTUS in the broader infant population.
The study further builds on the body of US real-world evidence demonstrating the high impact of BEYFORTUS. A prospective, population-based surveillance study published in JAMA Pediatrics showed a single dose of BEYFORTUS was 93% (95% CI, 82%-97%) effective in preventing RSV hospitalizations. The study included hospitalized infants under eight months old and accounted for key variables like age, illness onset, and high-risk conditions. Limitations included supply constraints resulting from high demand, a small proportion of hospitalized infants with acute respiratory infection receiving BEYFORTUS during the study period and potential RSV exposure prior to deployment of BEYFORTUS among some babies.
Prior to these US real-world studies, BEYFORTUS was evaluated in two pivotal trials. BEYFORTUS efficacy and safety were evaluated in two randomized, double-blind, placebo-controlled pivotal trials with the same primary and secondary endpoints versus placebo through 150 days post one dose: incidence of medically attended (includes all healthcare provider visits such as physician's office, urgent care, emergency room, and hospitalizations) RSV disease, including hospitalization.
BEYFORTUS significantly reduced the risk of serious RSV disease in term and late preterm healthy infants:
In Trial 04, BEYFORTUS demonstrated a relative risk reduction of 74.9% (95% CI: 50.6, 87.3; p<0.001). n=1,490 infants ≥35 wGA (placebo: 5.0% [25/496], BEYFORTUS: 1.2% [12/994]). BEYFORTUS dose: 50 mg for <5 kg; 100 mg for ≥5 kg
In Trial 03, BEYFORTUS demonstrated a relative risk reduction of 70.1% (95% CI: 52.3, 81.2; p<0.001). n=1,453 infants ≥29 to <35 wGA (placebo: 9.5% [46/484], BEYFORTUS: 2.6% [25/969]). BEYFORTUS dose: 50 mg regardless of weight
In both studies, the secondary endpoint was the incidence of serious RSV disease with hospitalization in term and preterm healthy babies through 150 days post one dose:
In Trial 04, BEYFORTUS demonstrated a relative risk reduction of 60.2% (95% CI: -14.6, 86.2; p=0.09). Primary Cohort: n=1,490 infants ≥35 wGA (placebo: 1.6% [8/496], BEYFORTUS: 0.6% [6/994])
In an exploratory, post hoc analysis of all infants (full study cohort) in Trial 04, BEYFORTUS demonstrated a relative risk reduction of 76.8% (95% CI: 49.4, 89.4). n=3,012 infants ≥35 wGA (placebo: 2.0% [20/1,003], BEYFORTUS: 0.4% [9/2,009])
In Trial 03, BEYFORTUS demonstrated a relative risk reduction of 78.4% (95% CI: 51.9, 90.3; p=0.0002). n=1,453 infants ≥29 to <35 wGA (placebo: 4.1% [20/484], BEYFORTUS: 0.8% [8/969])
The most common adverse reactions in Trial 04 and Trial 03 were rash (0.9%) and injection site reactions (0.3%).
About RSV
RSV is a highly contagious virus that can lead to serious respiratory illness for infants. Two out of three infants are infected with RSV during their first year of life and almost all children are infected by their second birthday. Most of the time RSV will cause a mild, cold-like illness. However, RSV is the most common cause of LRTD, including bronchiolitis and pneumonia, in infants. RSV LRTD is the leading cause of hospitalization in babies under one, with most hospitalizations for RSV occurring in healthy infants born at term. Each year in the US, an estimated 590,000 RSV cases in babies under one require medical care, including physician office, urgent care, emergency room visits and hospitalizations.
About BEYFORTUS
BEYFORTUS is a single-dose long-acting antibody designed to help prevent RSV LRTD in infants that extends through five months, the length of the typical RSV season in the US. For children undergoing cardiac surgery with cardiopulmonary bypass, an additional dose of BEYFORTUS is recommended as soon as the child is stable after surgery. An additional dose of BEYFORTUS is also indicated for children up to 24 months of age, regardless of body weight, who remain vulnerable to severe RSV disease through their second RSV season.
As a long-acting antibody provided directly to newborns and infants as a single dose, BEYFORTUS offers fast-acting protection to help prevent lower respiratory tract disease caused by RSV without requiring activation of the immune system. It has demonstrated a consistent safety profile across a broad infant population. BEYFORTUS administration can be timed to coincide with the RSV season.
BEYFORTUS has been approved for use in the US, the European Union, China, Japan, and many other countries around the world. Special designations to facilitate expedited development of BEYFORTUS were granted by several regulatory agencies, including Breakthrough Therapy Designation and Fast Track Designation from the US Food and Drug Administration; Breakthrough Therapy Designation and Priority Review designation by The China Center for Drug Evaluation under the National Medical Products Administration; access granted to the European Medicines Agency (EMA) PRIority MEdicines scheme and EMA accelerated assessment; Promising Innovative Medicine designation by the UK Medicines and Healthcare products Regulatory Agency; and BEYFORTUS has been named "a medicine for prioritized development" under the Project for Drug Selection to Promote New Drug Development in Pediatrics by the Japan Agency for Medical Research and Development.
INDICATION
BEYFORTUS is a prescription medicine used to help prevent a serious lung disease caused by Respiratory Syncytial Virus (RSV) in:
Newborns and babies under 1 year of age born during or entering their first RSV season.
Children up to 24 months of age who remain at risk of severe RSV disease through their second RSV season.
IMPORTANT SAFETY INFORMATION
Your child should not take BEYFORTUS if your child has a history of serious allergic reactions to nirsevimab-alip or any of the ingredients in BEYFORTUS.
Before your child receives BEYFORTUS, tell your healthcare provider about all of your child's medical conditions, including if your child:
has ever had a reaction to BEYFORTUS.
has bleeding or bruising problems. If your child has a problem with bleeding or bruises easily, an injection could cause a problem.
Tell your healthcare provider about all the medicines your child takes, including prescription and over-the-counter medicines, vitamins, and herbal supplements. Your infant should not receive a medicine called palivizumab if they have already received BEYFORTUS in the same RSV season.
Serious allergic reactions have happened with BEYFORTUS. Get medical help right away if your child has any of the following signs or symptoms of a serious allergic reaction:
swelling of the face, mouth, or tongue
difficulty swallowing or breathing
unresponsiveness
bluish color of skin, lips, or under fingernails
muscle weakness
severe rash, hives, or itching
The most common side effects of BEYFORTUS include rash and pain, swelling, or hardness at the site of your child's injection. These are not all the possible side effects of BEYFORTUS. Call your healthcare provider if you have questions about side effects.
Please see full
Prescribing Information
, including
Patient Information
, for more details.
MAT-US-2504102-v1.0-04/2025
About Sanofi
Sanofi is an R&D driven, AI-powered biopharma company committed to improving people's lives and delivering compelling growth. We apply our deep understanding of the immune system to invent medicines and vaccines that treat and protect millions of people around the world, with an innovative pipeline that could benefit millions more. Our team is guided by one purpose: we chase the miracles of science to improve people's lives; this inspires us to drive progress and deliver positive impact for our people and the communities we serve, by addressing the most urgent healthcare, environmental, and societal challenges of our time.
Sanofi is listed on EURONEXT: SAN andNASDAQ: SNY
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