Nirsevimab Protects Healthy Infants From RSV

Jake Remaly

March 03, 2022

A single injection of the experimental agent nirsevimab ahead of respiratory syncytial virus (RSV) season protects healthy infants from lower respiratory tract infections associated with the pathogen, according to the results of a phase 3 study.

A previously published trial showed that a single dose of nirsevimab was effective in preterm infants. The ability to protect all babies from RSV, which causes bronchiolitis and pneumonia and is a leading cause of hospitalization for this age group, "would be a paradigm shift in the approach to this disease," William Muller, MD, PhD, of the Lurie Children's Hospital of Chicago and a co-author of the study, said in a statement.

The primary endpoint of the study was medically attended lower respiratory tract infections linked to RSV. The single injection of nirsevimab was associated with a 74.5% reduction in such infections (P < .001), according to Muller's group, who published their findings March 2 in the New England Journal of Medicine.

Nirsevimab, a monoclonal antibody to the RSV fusion protein being developed by AstraZeneca and Sanofi, has an extended half-life, which may allow one dose to confer protection throughout a season. The only approved option to prevent RSV, palivizumab (Synagis), is used for high-risk infants, and five injections are needed to cover a viral season.

Nearly 1500 Infants in More Than 20 Countries Studied

To assess the effectiveness of nirsevimab in late-preterm and term infants, investigators at 160 sites randomly assigned 1490 babies born at a gestational age of at least 35 weeks to receive an intramuscular injection of nirsevimab or placebo.

During the 150 days after injection, medically attended RSV-associated lower respiratory tract infections occurred in 12 of 994 infants who received nirsevimab, compared with 25 of 496 babies who received placebo (1.2% vs 5%).

Six of 994 infants who received nirsevimab were hospitalized for RSV-associated lower respiratory tract infections, compared with 8 of 496 infants in the placebo group (0.6% vs. 1.6%; P = .07). The proportion of children hospitalized for any respiratory illness as a result of RSV was 0.9% among those who received nirsevimab, compared with 2.2% among those who received placebo.

Serious adverse events occurred in 6.8% of the nirsevimab group and 7.3% of the placebo group. None of these events, including three deaths in the nirsevimab group, was considered related to nirsevimab or placebo, according to the researchers. One infant who received nirsevimab had a generalized macular rash without systemic features that did not require treatment and resolved in 20 days, they said.

Antidrug antibodies were detected in 6.1% of the nirsevimab group and in 1.1% of the placebo group. These antidrug antibodies tended to develop later and did not affect nirsevimab pharmacokinetics during the RSV season, the researchers reported. How they might affect subsequent doses of nirsevimab is not known, they added.

In a separate report in the journal, researcher Joseph Domachowske, MD, SUNY Upstate Medical University, Syracuse, New York, and colleagues described safety results from an ongoing study of nirsevimab that includes infants with congenital heart disease, chronic lung disease, and prematurity.

In this trial, infants received nirsevimab or palivizumab, and the treatments appeared to have similar safety profiles, the authors reported.

Other approaches to RSV protection include passive antibodies acquired from maternal vaccination in pregnancy and active vaccination of infants.

The publication follows news last month that GlaxoSmithKline is pausing a maternal RSV vaccine trial, which "had the same goal of protecting babies against severe RSV infection," said Louis Bont, MD, PhD, with University Medical Center Utrecht, the Netherlands.

RSV infection is one of the deadliest diseases during infancy, and the nirsevimab trial, conducted in more than 20 countries, is "game-changing," Bont told Medscape Medical News. Still, researchers will need to monitor for RSV resistance to this treatment, he said.

Whether nirsevimab prevents the development of reactive airway disease and asthma is another open question, he said.

"Finally, we need to keep in mind that RSV mortality is almost limited to the developing world and it is unlikely that this novel drug will become available to these countries in the coming years," Bont said. "Nevertheless, nirsevimab has the potential to seriously decrease the annual overwhelming number of RSV infected babies."

Nirsevimab may have advantages in low- and middle-income countries, including its potential to be incorporated into established immunization programs and to be given seasonally, said Amy Sarah Ginsburg, MD, MPH, of the University of Washington, Seattle. "However, cost remains a significant factor as does susceptibility to pathogen escape," she said.

MedImmune/AstraZeneca and Sanofi funded the nirsevimab studies. UMC Utrecht has received research grants and fees for advisory work from AstraZeneca for RSV-related work by Bont.

N Engl J Med. Published online March 2, 2022. Abstract, Correspondence

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