CDC data: nirsevimab was about 75% effective against RSV hospitalisation in high-risk toddlers' second season

Real-world data presented at the IDWeek meeting suggest that nirsevimab (Beyfortus), a long-acting antibody against respiratory syncytial virus (RSV), protects high-risk children in their second RSV season, MedPage Today reported on 23 October 2026.

Background

In the US, nirsevimab is recommended for all infants in their first RSV season and for certain children aged 8–19 months entering their second season who are at higher risk of severe disease — for example those with chronic lung disease of prematurity, severe immunocompromise, some children with cystic fibrosis, and all American Indian and Alaska Native children, according to CDC’s advisory committee documents. That second-season recommendation relied largely on drug-level data rather than direct efficacy trials.

What the study found

• The case-control study, presented by Angela Campbell of the CDC, included nirsevimab-eligible children aged 8–23 months hospitalised with respiratory symptoms.
• RSV tested positive in 20% of children who had received nirsevimab versus 42% of those who had not.
• Adjusted effectiveness against RSV-associated hospitalisation was 75% — 86% when the antibody was given within 60 days before symptoms and 66% when given earlier.
• “Overall, these estimates support the initial recommendation,” Campbell said.

Limitations

This is an observational case-control analysis presented at a conference and not yet published in a peer-reviewed journal, so results may change and unmeasured differences between groups could affect the estimates. The lower figure for earlier dosing suggests protection wanes with time. A separate peer-reviewed study of re-immunisation with a second dose found a highly uncertain estimate (42%, 95% CI −25% to 73%). Parents should ask their child’s doctor whether their child qualifies.