Nirsevimab reduces risk for infant RSV

Key takeaways:

• Only one infant with respiratory syncytial virus (RSV) lower respiratory tract disease (LRTD) in the nirsevimab group was hospitalized.
• The risk for RSV LRTD was reduced by 71% among infants taking nirsevimab.

BOSTON — Infants who took nirsevimab had a reduced risk for respiratory syncytial virus lower respiratory tract disease, according to an abstract presented at the American College of Allergy, Asthma & Immunology Annual Scientific Meeting.

“We assessed the effectiveness of routinely administered nirsevimab in Kaiser Permanente Northern California, or KPNC, to all eligible infants aged less than 8 months during the 2023 and 2024 RSV season,” Nicky Klein, MD, PhD, professor at Kaiser Permanente Bernand J. Tyson School of Medicine, said during her presentation.

These healthy full-term infants ( 37 weeks’ gestation) were born on or after April 1, 2023. Those who received palivizumab, a positive respiratory syncytial virus (RSV) test prior to study follow-up or whose mothers received an RSV vaccine were excluded.

The primary outcomes included the first polymerase chain reaction (PCR)-confirmed RSV lower respiratory tract disease (LRTD) diagnosis and the number of medical encounters as a result of the diagnosis. Outcomes between Oct. 19, 2023, and April 30, 2024, were included.

In total, 15,647 infants (50.7% boys; 28.4% white; 29.9% Hispanic) received nirsevimab (Beyfortus; AstraZeneca, Sanofi), with 87.5% administered in an outpatient setting, and 16,253 (50.8% boys; 32.4% white; 32.2% Hispanic) did not receive the drug.

“The demographic characteristics and the racial and ethnic characteristics represent the diversity of Northern California and similarity between both infants who did and did not receive nirsevimab,” Klein said.

A PCR-confirmed RSV LRTD diagnosis was seen in 35 infants who received nirsevimab compared with 462 who did not, for an estimated treatment effectiveness of 87.2% (95% CI, 81.7%-91.1%).

In terms of the number of medical encounters as a result of the diagnosis, only one out of the 35 PCR-confirmed RSV LRTD-diagnosed infants who received nirsevimab was hospitalized. This compared with 65 in the non-nirsevimab group for an adjusted odds ratio of 0.11 (95%, CI 0.01-0.85).

Further, the total medical encounters among the nirsevimab infants was 75 compared with 1,241 encounters among non-nirsevimab infants. This equated to a mean number of medical encounters during an RSV LRTD episode of 2.143 with nirsevimab and 2.686 without, for an adjusted difference in means of –0.86 (95% CI, –1.36 to –0.36).

“Nearly half of eligible KPNC healthy term infants received nirsevimab during the 2023 to 2024 season,” Klein said. “In this large study, nirsevimab reduced the risk of RSV LRTD amongst healthy term infants by 87% across all health care settings.”

Klein further explained that nirsevimab reduced the risk for PCR-confirmed RSV with or without LRTD by 71% compared with untreated infants.

“Those who had RSV LRTD after nirsevimab had significantly fewer medical encounters and were less likely to be hospitalized,” she said.