Nirsevimab cuts risk of hospitalization for RSV-associated bronchiolitis

The ENVIE* study demonstrates the real-world effectiveness of nirsevimab against hospitalization for bronchiolitis associated with respiratory syncytial virus (RSV) among infants <12 months of age in France.

“In this real-world study, we estimated the post licensure effectiveness of nirsevimab therapy against hospitalization for RSV-associated bronchiolitis among infants <12 months of age and found an overall effectiveness of 83 percent,” said the researchers.

“This level of effectiveness was consistent across age groups. In addition, nirsevimab therapy was effective against the most severe forms of RSV-associated bronchiolitis,” they continued.

The effectiveness of nirsevimab against RSV-associated bronchiolitis resulting in critical care and in ventilatory support was 69.6 percent and 67.2 percent, respectively. In infants with at least one risk factor for bronchiolitis, the effectiveness of nirsevimab was 64.8 percent; however, this analysis was limited by the small sample size. [N Engl J Med 2024;391:144-154]

“These results need to be put in perspective with the findings of the prelicensure phase III trials,” the researchers pointed out, noting that the current effectiveness rates seem to be higher than those observed in the MEDLEY and MELODY trials but align with those reported in HARMONIE.

In France, nirsevimab implementation started on September 15, 2023, and enrolment for ENVIE was stopped on December 10, 2023. Hence, ENVIE evaluated the efficacy of nirsevimab within 3 months following its implementation. Such was the case in HARMONIE, which evaluated results on day 90 post nirsevimab administration. [N Engl J Med 2023;389:2425-2435] In MEDLEY and MELODY however, results were evaluated on day 150. [N Engl J Med 2022;386:837-846; N Engl J Med 2022;386:892-894]

“Given that the protection conferred by nirsevimab may decrease over time, this situation may have contributed to the higher effectiveness found in our study than in MEDLEY and MELODY,” the researchers explained.

A reasonable alternative to palivizumab

Of the 1,035 infants included in the study, 690 were case patients (median age 3.1 months) and 345 were matched controls (median age 3.4 months). Case patients were infants <12 months of age hospitalized for RSV-associated bronchiolitis between October 15 and December 10, 2023, while controls were those who had clinical visits to the same hospitals for conditions that were not related to RSV. Sixty case patients (8.7 percent) and 97 control patients (28.1 percent) had previously received nirsevimab.

Nirsevimab is a monoclonal antibody against RSV that has enhanced neutralizing activity and an extended half-life in vivo. It has gained approvals from the EMA in November 2022 and the FDA in July 2023. [Sci Transl Med 2017;9:eaaj1928; MMWR Morb Mortal Wkly Rep 2023;72:920-925]

Prior to the approval of nirsevimab, palivizumab was the only existing prophylactic agent against RSV. [Pediatrics 2014;134:415-420] “[However,] palivizumab requires monthly injections throughout the RSV season to provide sustained protection and, on a population basis, has only a limited effect on the incidence of RSV-associated hospitalizations,” the researchers pointed out.

The current findings imply that nirsevimab may be a reasonable alternative to palivizumab in children with risk factors for severe bronchiolitis. [Lancet Child Adolesc Health 2023;7:180-189]

“[Taken together,] this real-world study evaluating the effectiveness of nirsevimab within 3 months of nationwide implementation indicate that nirsevimab prophylaxis was effective against RSV-associated bronchiolitis leading to hospitalization among infants <12 months of age, including those with severe cases that led to paediatric intensive care unit admission and ventilatory support,” said the researchers.

Given the observational case-control study design and the very early evaluation of nirsevimab (ie, after the start of the national programme), studies in other settings and with longer durations are warranted to corroborate the findings.