RSV Protection Lasts Beyond Baby's First Year, New Study Shows—Here's What That Means

A new study published in The Lancet Infectious Diseases shows that infants who received the RSV immunization Beyfortus (nirsevimab) during their first RSV season experienced significantly fewer RSV-related hospitalizations in their second season, suggesting the protection extends well beyond the initial year of life. This finding challenges the assumption that RSV protection is temporary and opens new possibilities for long-term respiratory health in infants.

How Long Does RSV Protection Actually Last?

Researchers in Galicia, Spain conducted the NIRSE-GAL study, the first real-world population study to track RSV immunization benefits across two consecutive seasons. The study followed 11,796 infants (out of 12,492 eligible) with a 94.4% coverage rate. During the first RSV season, infants who received Beyfortus showed an 85.9% reduction in RSV-related lower respiratory tract infection hospitalizations. But the truly surprising finding came when researchers looked at the second year: infants who had been immunized during their first season experienced 55.3% fewer RSV-related hospitalizations in their second season compared to what would have been expected based on historical data.

"This universal RSV immunization program with Beyfortus showed decreased RSV-related hospitalizations and outpatient illness burden during the first season, with persistent impact seen on RSV hospitalizations through the second season," said Federico Martinón-Torres, Head of Pediatrics at Santiago University Hospital in Spain and principal investigator of the study. "These results offer compelling population-based data to inform infant immunization strategies and economic evaluation models."

Why Does Protection Extend Into Year Two?

The mechanism behind this extended protection appears to involve lung development. By preventing severe RSV infections during the first months of life—a critical period when lungs are still developing—infants may be less prone to subsequent respiratory infections. The study found that infants who had previously been hospitalized for RSV showed particularly dramatic improvements: those who received Beyfortus had a 78.2% reduction in RSV-related rehospitalizations and a 62.4% reduction in lower respiratory tract infection rehospitalizations during the second season.

Beyond hospitalizations, the immunization program reduced the burden on healthcare systems and families during the first RSV season. The study documented several important reductions in primary care visits:

• Acute respiratory infections: A 30.8% reduction in first consultations for acute bronchitis or bronchiolitis
• Lower respiratory tract infections: A 33.4% reduction in consultations for lower respiratory tract infections
• Breathing problems: A 27.7% reduction in consultations for wheezing or asthma

These reductions suggest that early protection against RSV-related damage to the lungs may have lasting beneficial effects on respiratory health throughout infancy and early childhood.

How Does Beyfortus Compare to Other RSV Prevention Methods?

Recent research from the United States provides important context for understanding how different RSV prevention strategies stack up. A population-based surveillance study published in JAMA Pediatrics assessed the effectiveness of both RSV prevention approaches during the 2024-25 season across seven pediatric medical centers. The study found that nirsevimab (Beyfortus) was 81% effective against RSV-associated hospitalization in infants, with protection remaining at 77% for 130 to 210 days after vaccination. In comparison, maternal RSV vaccination showed 64% effectiveness against medically attended acute respiratory infection and 70% effectiveness against hospitalization.

The real-world impact has been substantial. Overall hospitalization rates were reduced by an estimated 41% to 51% among infants aged 11 months or younger compared with rates from 2017-20, before these products were introduced. The highest reduction—between 56% to 63%—occurred in newborns aged 0 to 2 months. "Both maternal RSV vaccine and nirsevimab were estimated to be effective at protecting infants from RSV-associated hospitalizations in their first RSV season," the researchers noted, "RSV-associated hospitalization rates in newborns and infants aged 0 to 11 months were reduced by up to half compared to seasons before these products were introduced."

What Is RSV and Why Should Parents Care?

Respiratory syncytial virus (RSV) is a highly contagious virus that can lead to serious respiratory illness in infants. It remains a leading cause of hospitalization in all infants, with most hospitalizations occurring in otherwise healthy infants born at term. 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. Globally, RSV causes approximately 33 million cases of acute lower respiratory infections annually, leading to more than three million hospitalizations and an estimated 26,300 in-hospital deaths of children younger than five years.

Beyfortus (nirsevimab) is the first RSV immunization designed to help protect all infants through their first RSV season, including those born healthy at term or preterm, and those with health conditions that make them vulnerable to RSV disease. The medication is also approved for children up to 24 months of age who remain vulnerable to severe RSV disease through their second RSV season. With an extended half-life of 71 days, Beyfortus is a long-acting monoclonal antibody—a type of protein that provides rapid protection without requiring activation of the immune system. Since its launch, over 11 million infants have been immunized with Beyfortus across more than 45 countries.

The Spanish study adds to a growing body of real-world evidence supporting RSV immunization programs. More than 50 real-world studies have now evaluated the effectiveness of Beyfortus, including data from more than 400,000 infants who were immunized. As RSV activity remains elevated in many areas of the United States, with particularly high hospitalization rates among infants less than one year old, these findings provide reassuring evidence that early immunization offers protection that extends well into the second year of life.