Nirsevimab Reduces Risk for Severe RSV in AI/AN Children

Use of nirsevimab was associated with an approximately 80% reduction in illness due to respiratory syncytial virus (RSV) infections among American Indian and Alaskan Native (AI/AN) infants, based on data from more than 700 children younger than 20 months.

AI/AN children have disproportionately high rates of hospitalization for RSV in part because of poor living conditions such as indoor air pollution and lack of in-home plumbing, wrote Brian Lefferts, MPH, of the Yukon-Kuskokwim Health Corporation (YKHC), Bethel, Alaska, and colleagues.

The YKHC, a tribal health organization, administered nirsevimab, a preventive monoclonal antibody, to approximately half (48%) the children younger than 20 months living in the Yukon-Kuskokwim Delta region of Alaska between October 1, 2023, and April 30, 2024.

In August 2023, the Centers for Disease Control and Prevention’s (CDC’s) Advisory Committee on Immunization Practices recommended a long-acting monoclonal antibody (nirsevimab) for all infants younger than 8 months born during or entering their first RSV season and for children aged 8-19 months entering their second season who are at an increased risk for severe RSV illness, including all AI/AN children, said corresponding author Heather M. Scobie, PhD, of the CDC, in an interview. “This evaluation in Alaska’s Yukon-Kuskokwim Delta region provided the first real-world estimates of nirsevimab effectiveness among AI/AN children in their first and second RSV seasons,” she said.

In a study published in the CDC’s Morbidity and Mortality Weekly Report, the researchers reviewed data from 472 children with medically attended acute respiratory illness between October 23, 2023, and June 30, 2024. Of these, 48% had received nirsevimab at least 7 days previously, with a median of 91 days before the visit.

Nirsevimab was 76% effective against RSV illness and 89% effective against RSV hospitalization for children in their first RSV season and 88% effective against illness RSV illness for children in their second season. Effectiveness against hospitalization in the second season was not estimated because of small numbers (15 children).

“Consistent with previous studies among infants in their first RSV season, this evaluation documented nirsevimab effectiveness in an AI/AN population known to be at increased risk for severe RSV illness and at a longer median interval from nirsevimab receipt (91 days),” Scobie told Medscape Medical News. “The nirsevimab effectiveness observed among AI/AN in their first and second RSV seasons was similar to that observed in previous studies among US infants in their first RSV season,” she said.

The findings were limited by several factors, including the clinician-directed RSV testing that might have excluded children with milder illness, and by the low RSV incidence during the study period, Scobie noted. Other limitations included a lack of data on nirsevimab dosage and potential lack of generalizability of the data to other populations in other locations, she said.

However, the take-home message for clinicians is to talk to parents and caregivers about protecting young children against severe RSV and to recommend nirsevimab to all infants younger than 8 months whose mothers were not vaccinated against RSV during pregnancy, Scobie told Medscape Medical News. The CDC continues to recommend nirsevimab for children aged 8-19 months who are at an increased risk for severe RSV, including all AI/AN children, she said.

As for additional research, “An evaluation of nirsevimab effectiveness against hospitalization for eligible children in their second RSV season would be helpful, as would evaluations that are able to further assess effectiveness by time since nirsevimab receipt or nirsevimab dosage,” Scobie added.

Early Protection Helps

“As we head into RSV season, it is important to remember that we now have powerful tools, either as active RSV vaccination of the mother prenatally or passive nirsevimab immunity given to the infant, to prevent the number-one cause of hospitalization in young children,” said Tim Joos, MD, a Seattle-based clinician with a combination internal medicine/pediatrics practice, in an interview.

“It was interesting to see in the data that the number of children who had received nirsevimab and still got RSV started climbing toward the end of the season likely reflecting waning passive immunity over time,” Joos told Medscape Medical News.

Looking ahead, “It will be interesting to see if the RSV infection season itself shifts in response to this seasonal passive immunity approach,” said Joos, who was not involved in the study. “We saw shifts in the RSV season during the COVID pandemic years, likely in response to social distancing and masking; future timing recommendations for nirsevimab may have to adapt to a changing RSV season,” he noted.

“Nevertheless, it is clear that the later a child gets RSV, the better the clinical outcome, and protecting children from RSV in the first year or two of life is a worthwhile goal,” Joos said.

The study received no outside funding. Scobie had no personal financial conflicts to disclose. Joos had no financial conflicts of interest but serves on the editorial advisory board of Pediatric News.