Monoclonal antibody halves hospitalizations of children younger than 6 months old

A single dose of the long-acting antibody nirsevimab to infants can halve hospitalizations for bronchiolitis.

This is the result of a study involving the Università Cattolica del Sacro Cuore, Rome campus—Fondazione Policlinico Universitario Agostino Gemelli IRCCS, coordinated by Universitat Politècnica de Catalunya (UPC), Catalonia, Children’s Emergency Department, Leicester Royal Infirmary and University of Edinburgh, the first to analyze a “real world” case study.

Developed to prevent respiratory syncytial virus infections, the drug has been approved at the European level to protect infants in their first season of exposure to the virus.

The work was published in The Lancet Regional Health—Europe journal and was coordinated by Dr. Danilo Buonsenso, researcher in General and Specialist Pediatrics at the Faculty of Medicine of the Catholic University and pediatrician at the Pediatric Infectious Diseases Unit of the Fondazione Policlinico Gemelli IRCCS.

Buonsenso explains, “Now, for the first time, a real-world study has analyzed the concrete impact of nirsevimab by comparing European countries with different health policies: Catalonia (Spain), where the drug was introduced in 2023-2024, and some areas of the UK and Rome (Italy), where it had not yet been adopted.”

Bronchiolitis is an acute viral infection that affects the respiratory system of children under one year of age mainly in the first six months of life with greater frequency between November and March. It is often associated with respiratory syncytial virus infection (in about three out of four cases) that can cause respiratory failure, especially in children under one year of age and among babies under six months old.

But other viruses can also be the cause: metapneumovirus, coronavirus, rhinovirus, adenovirus, influenza and parainfluenza viruses. Infection results from transmission primarily by direct contact with infected secretions.

The data, collected from 68 Catalan hospitals and five hospitals in the United Kingdom and Italy, show a clear result: in children under 6 months in Catalonia, hospitalizations for bronchiolitis have almost halved compared to the average of previous seasons.

Emergency room admissions for the same age group were also significantly reduced. In contrast, no significant reduction emerged in the other European centers where nirsevimab was not administered.

The drug’s effect was less pronounced in older children (between 6 and 23 months), suggesting that the greatest efficacy is concentrated in the first few months of life. The authors also emphasize the need for larger, internationally coordinated studies, not least to assess the economic sustainability of introducing nirsevimab on a large scale.

The study represents an important step in assessing the real effectiveness of new preventive strategies against RSV, comparing, for the first time, countries with different approaches to its implementation, Buonsenso concludes.