Summary of the National Advisory Committee on Immunization (NACI) Statement on the Prevention of Respiratory Syncytial Virus (RSV) in Infants.

Background: Immunization programs for the prevention of respiratory syncytial virus (RSV) in infants have been available in Canada since the authorization of palivizumab in 2002. However, these programs have been limited to only those infants at highest risk for severe RSV disease. The authorization of new passive immunizing products to prevent RSV, including a new monoclonal antibody (nirsevimab) and a vaccine administered in pregnancy (RSV pre-fusion stabilized F protein; RSVpreF) offers the opportunity to prevent RSV in more Canadian infants. The objective of this article is to summarize guidance from the National Advisory Committee on Immunization (NACI) on the prevention of RSV in infants. Methods: NACI established key policy questions and performed an evidence review and synthesis. NACI made evidence-based recommendations in consideration of the burden of illness to be prevented, safety and efficacy of the new immunizing products, economic evidence and ethics, equity, feasibility, and acceptability. Results: Nirsevimab and RSVpreF offer protection against severe outcomes of RSV disease, including hospitalization and intensive care unit admission. Nirsevimab protection may be slightly higher and may last longer than protection offered by RSVpreF. Nirsevimab and RSVpreF also have a similar frequency of adverse reactions for both pregnant and infant participants. The RSVpreF vaccine may increase the risk of severe local adverse events compared to placebo for pregnant recipients. In RSVpreF clinical trials, an imbalance was observed in late preterm birth between RSVpreF and placebo recipients. It is unclear whether there is a causal relation with the vaccine as the currently available data is inconclusive. Conclusion: Based on new evidence, NACI recommends building towards a universal RSV immunization program for all infants. Currently, nirsevimab is preferred over RSVpreF. Program introduction could occur in stages depending on access to supply, cost effectiveness, and affordability of available options.