Nirsevimab protects infants against hospitalization from RSV

Key takeaways:

• The efficacy of nirsevimab ranged from 74.2% to 89.6% across three countries.
• Additionally, no safety concerns were identified in the trial.

The monoclonal antibody nirsevimab prevented hospitalizations for respiratory syncytial virus-associated disease among infants “in conditions that approximated real-world settings,” researchers wrote in The New England Journal of Medicine.

“RSV illnesses and their sequelae account for a large proportion of primary care pediatric workload over the winter months,” Simon Royal, MPH, MRCGP, an honorary assistant professor in the School of Medicine at the University of Nottingham in the United Kingdom, told Healio. “Assessing ill babies takes a lot of time and can be stressful for everyone involved. Anything which reduces the number of infants affected by these diseases should help to free up valuable time and improve outcomes for patients.”

The FDA approved nirsevimab (Beyfortus, AstraZeneca and Sanofi) for the prevention of RSV disease in newborns and infants in July.

The CDC recommends nirsevimab use for infants aged younger than 8 months born during or entering their first RSV season, at an intramuscular injection of 50 mg for infants weighing less than 5 kg and100 mg for infants weighing 5 kg or more. Children aged 8 to 19 months who are entering their second RSV season and are at an increased risk for severe RSV disease are recommended to receive one dose at 200 mg.

Recent research has suggested nirsevimab could offer protection for a period longer than the typical 5-month RSV season.

Royal and colleagues tested the efficacy of the treatment in the phase 3b HARMONIE trial, which randomly assigned infants to nirsevimab (n = 4,037) or standard care (n = 4,021) “in conditions similar to those in routine clinical practice.”

“Nirsevimab has an extended half-life of approximately 71 days,” they wrote. “It therefore has the potential to provide protection to all infants if it is administered in a program similar to programs used for vaccines.”

Infants in the trial were aged 12 months or younger, born at a gestational age of at least 29 weeks and were entering their first RSV season in France, Germany or the U.K.

The researchers found that 0.3% and 1.5% of infants in the nirsevimab and standard care groups were hospitalized for RSV-associated lower respiratory tract infection, respectively, yielding an efficacy of 83.2% (95% CI, 67.8-92) for nirsevimab.

Meanwhile, 0.1% of infants in the nirsevimab group and 0.5% of infants in the standard care group were hospitalized for very severe RSV-associated lower respiratory tract infection, with an efficacy rate of 75.7% (95% CI, 32.8-92.9) for nirsevimab.

Overall, the efficacy of nirsevimab against hospitalization for RSV disease was:

• 89.6% (95% CI, 58.8-98.7) in France;
• 74.2% (95% CI, 27.9-92.5) in Germany; and
• 83.4% (95% CI, 34.3-97.6) in the U.K.

Royal and colleagues identified treatment-related adverse events in 2.1% of infants in the nirsevimab group.

“No substantial safety concerns were identified in this trial, nor have they been identified across the growing clinical experience with nirsevimab, which now includes more than 7,500 infants,” they wrote.

Royal pointed out more research is warranted “to see whether immunization against RSV reduces the incidence of respiratory diseases later in childhood.”

“Economic modelling is needed to accurately establish the cost effectiveness of an immunization program,” he said.

The researchers noted that the trial was limited because of its short assessment and safety follow-up duration of around 3 months. Additionally, the trial design did not include blinding, which may or may not have impacted health care-seeking behavior.

Ultimately, “HARMONIE has shown that nirsevimab is safe and easy to administer to all babies aged 0 to 1 and it could slot in easily with the current routine schedule or be given at mass clinics,” Royal said.