Nirsevimab, a recently approved monoclonal antibody injection, has demonstrated remarkable efficacy in protecting infants from severe respiratory syncytial virus (RSV) infections. A new study published in JAMA Pediatrics reported a 93% effectiveness in preventing RSV-related hospitalizations. This finding underscores the potential of nirsevimab to significantly reduce the burden of RSV, the leading cause of infant hospitalization in the United States.
The study compared three RSV seasons prior to nirsevimab's approval to the 2023-2024 season, revealing a substantial impact on hospitalization rates. Nirsevimab, marketed as Beyfortus, provides passive immunity by delivering lab-made antibodies that block RSV from entering cells, offering immediate protection lasting several months.
Real-World Impact
Data from Ireland further supports nirsevimab's effectiveness, with official figures showing a 94% drop in RSV-related hospitalizations among infants under one year old after the treatment's rollout. Hospitalizations fell from 413 cases in 2023 to just 24 cases in 2024, while cases requiring intensive care plummeted by 92%, from 64 to just five.
In Alaska's Yukon-Kuskokwim Delta, a region with historically high rates of infant RSV hospitalization, nirsevimab reduced RSV-related hospitalizations by 89% during its first season of administration, according to a CDC report. The Yukon-Kuskokwim Health Corp. administered nirsevimab to 756 children younger than 20 months old, approximately half of the region's population in that age group.
Clinical Trial Data
The HARMONIE trial, conducted across the UK, France, and Germany, involved over 8,000 infants and found that nirsevimab reduced RSV-related hospitalizations by 83% compared to standard care. There were only 11 hospital admissions among treated infants versus 60 in the control group. This research aligns with real-world data from Spain.
Nirsevimab vs. Maternal Immunization
While some countries, like the UK, have opted for maternal immunization against RSV, data suggests that this approach may have limitations. UK Health Security Agency (UKHSA) data shows no significant reduction in RSV hospitalizations among children under five this winter compared to previous years. Critics argue that maternal immunization alone leaves gaps in protection, as not all newborns receive the same level of immunity.
Addressing RSV Burden
Each year in the United States, 2 to 3 out of every 100 infants under 6 months old are hospitalized for RSV, according to the CDC. These cases often require supplemental oxygen, IV fluids, and ventilator support. Nirsevimab offers a crucial preventative measure, particularly given that, prior to its approval, there were no widespread strategies for preventing RSV in infants.
Dr. Simon Drysdale, a co-leader of the HARMONIE trial, emphasized the treatment’s impact: “The thousands of winter hospital admissions caused by RSV are highly distressing for families and place a huge burden on health services. This groundbreaking study shows the potential of nirsevimab to transform RSV prevention.”
Recommendations and Availability
The CDC recommends that eligible babies receive nirsevimab just before the start of their first RSV season or within a week of birth if born during RSV season. Select older children are also recommended to receive the drug before their second RSV season. While initial supply issues have been reported, increased availability and wider adoption of nirsevimab could further reduce RSV hospitalizations in future seasons.
