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#361 Preventing RSV Infections in Infants

How safe and effective are monoclonal antibodies to prevent respiratory syncytial virus (RSV) infections in infants?

In high-risk infants (premature and/or congenital heart or lung conditions), palivizumab (4-5 doses monthly during RSV season) reduces RSV hospitalization (4.5% versus 10% placebo).  Nirsevimab (one dose) reduces RSV hospitalizations in healthy premature infants (0.8% versus 4%) and term infants (0.3-0.4% versus 1.5-2.0%). Side effects are similar to placebo.

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  • From highest quality systematic review or key randomized controlled trials (RCTs). Comparisons statistically different unless indicated.
  • Palivizumab: 4-5 doses monthly during RSV season;
    • Systematic review (5 RCTs, 3443 infants)1 with two dominant placebo-controlled RCTs: Infants born <35 weeks or with bronchopulmonary dysplasia2 or congenital heart disease.3 At two years:
      • RSV hospitalization: 4.4% versus 9.8% (placebo), relative risk reduction (RRR)=55%; number needed to vaccinate (NNV)=19.
      • Mortality: 1.3% versus 2.3% placebo (not statistically different).
  • Nirsevimab: Single-dose; given before/during RSV season.4-7
    • Versus placebo:
      • Premature, healthy: 1453 infants (born between 29-35 weeks).4 At 150 days:
        • RSV hospitalization: 0.8% versus 4.1% (placebo); RRR=81%; NNV=3.
        • Mortality (after one year) 0.2% versus 0.6% placebo, not statistically different (PEER calculation).
      • Term/near-term, healthy: 3012 infants.5,6 At 150 days:
        • RSV hospitalizations: 0.4% versus 2.0% (placebo): RRR=78%; NNV=63.
        • Deaths (after one year): 3 nirsevimab versus 0 placebo (none attributed to nirsevimab or RSV).
    • Versus no treatment (unblinded):
      • 8058 infants: 85% born ≥37 weeks.7 At three months:
        • RSV hospitalizations: 0.3% versus 1.5% (no treatment); RRR=82%, NNV=82.
        • One-year data forthcoming.
  • Adverse events: Similar between palivizumab, nirsevimab and placebo.1,4-8
  • Limitations: Many RCT authors were shareholders/employees of industry funder.4,5

  • In Canada, RSV responsible for ~2,500 childhood hospitalizations annually.9 Of those hospitalized:
    • ~80% had no underlying medical conditions, were <2 years old.10
    • Mortality: 2/1000.
  • In Canada, palivizumab recommended for high-risk infants:11
    • Prematurity (<30 weeks).
    • <2 years with chronic lung/congenital heart disease.
    • Living in remote/northern communities.
  • Nirsevimab:
    • Anticipated Canadian availability/guidance/pricing:12 2024
    • Versus palivizumab: Less costly (per patient).13
    • In US, recommended for all infants <8 months entering first RSV season.10
      • Second season: for high-risk infants (8-19 months).

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  • Samantha S. Moe PharmD
  • Sam Wong MD FRCPC
  • Michael R Kolber MD CCFP MSc

1. Garegnani L, Styrmisdottir L, Rodriguez P. Cochrane Database Syst Rev. 2021; 11:CD013757.

2. The IMpact-RSV Study Group. Pediatrics. 1998; 102(3):531-7

3. Feltes TF, Cabalka AK, Meissner HC, et al. J Pediatr. 2003; 143: 532-40.

4. Griffin MP, Yuan Y, Takas T, et al. N Engl J Med. 2020; 383:415-25.

5. Hammitt LL, Dagan R, Yuan Y, et al. N Engl J Med. 2022; 386:837-46.

6. Muller WJ, Madhi SA, Nuñez BS, et al. N Eng J Med. 2023; 388;16: DOI:10.1056/NEJMc2214773.

7. Drysdale SB, Cathie C, Flamein F, et al. N Eng J Med. 2023; 389;2425-35.

8. Domachowske J, Madhi SA, Simoes EAF, et al. N Eng J Med. 2022; 386(9):892-4.

9. Bourdeau M, Vadlamudi NK, Bastien N, et al. JAMA network open. 2023; 6(10):e2336863.

10. Jones JM, Fleming-Dutra KE, Prill MM, et al. MMWR Morb Mortal Wkly Rep. 2023; 72:920-925.

11. Public Health Agency of Canada. National Advisory Committee on Immunization: Recommended use of palivizumab to reduce complications of respiratory syncytial virus infection in infants. 2022. Available at: Accessed December 13, 2023.

12. CADTH. Nirsevimab (Beyfortus) for respiratory syncytial virus prevention in neonates and infants. 2023. Available at: Accessed March 6, 2023.

13. CADTH. Cost-effectiveness of nirsevimab for prevention of respiratory syncytial virus outcomes in infants. 2023. Available at: Accessed March 6, 2023.

Authors have no conflicts to declare.