A case-control study showed protective benefits comparable to those seen in preapproval trials.

Nirsevimab (Beyfortus; a long-acting monoclonal antibody administered as a single intramuscular dose) was US Food and Drug Administration-approved for preventing respiratory syncytial virus (RSV) illness in infants and toddlers in July 2023. Industry-sponsored randomised trials have shown efficacy in the range of 70% to 80% (NEJM JW Pediatr Adolesc Med Sep 2020 and N Engl J Med 2020; 383: 415-425; NEJM JW Gen Med Mar 8 2022; and N Engl J Med 2022; 386: 837-846; and NEJM JW Infect Dis Jan 3 2024; and N Engl J Med 2023; 389: 2425-2435). Nirsevimab was administered widely in the USA during the 2023 to 2024 RSV season.

To examine real-world effectiveness of nirsevimab, French researchers conducted a prospective case-control study in autumn 2023. Infants younger than 12 months who were admitted to six French hospitals with RSV bronchiolitis (cases) were compared with infants who presented with unrelated complaints (controls). Case and controls were matched on age, time of presentation and study location. Cases were significantly less likely than controls to have received nirsevimab; the overall adjusted estimated efficiency to prevent hospitalisation for RSV bronchiolitis was 83%, and it was similar for infants younger or older than 3 months.

Comment: These results closely match those of the preapproval trials. Because protective effects from a single injection are expected to wane, a longer observational trial would be helpful. Regardless, these findings should encourage clinicians to strongly recommend nirsevimab for infants. At my institution, I have observed that a high level of parental hesitancy, combined with nirsevimab supply shortages, appeared to result in suboptimal uptake.

Nolan J. Mischel, MD, Core Family Medicine Faculty member, John Peter Smith Hospital; Assistant Professor of Medicine, Texas Christian University Burnett School of Medicine, Fort Worth, USA.

Assad Z, et al. Nirsevimab and hospitalization for RSV bronchiolitis. N Engl J Med 2024; 391: 144-154.

This summary is taken from the following Journal Watch titles: Infectious Diseases, Pediatrics and Adolescent Medicine.