Safety and Immunogenicity of 3 Formulations of an Investigational Respiratory Syncytial Virus Vaccine in Nonpregnant Women: Results from 2 Phase 2 Trials

Background Respiratory syncytial virus (RSV) causes bronchiolitis and pneumonia in neonates and infants. RSV vaccination during pregnancy could boost preexisting neutralizing antibody titers, providing passive protection to newborns. Methods Two observer-blinded, controlled studies (RSV F-020 [clinical trials registration NCT02360475] and RSV F-024 [NCT02753413]) evaluated immunogenicity and safety of an investigational RSV vaccine in healthy, nonpregnant 18-45-year-old women. Both studies used a licensed adult formulation of combined tetanus toxoid-diphtheria toxoid-acellular pertussis (Tdap) vaccine as a control. RSV F-020 evaluated immunogenicity and safety: participants were randomized (1:1:1:1) to receive 1 dose of RSV-prefusion F protein (PreF) vaccine containing 30 μg or 60 μg of nonadjuvanted RSV-PreF, 60 μg of aluminum-adjuvanted RSV-PreF, or Tdap. RSV F-024 evaluated safety: participants were randomized 1:1 to receive 1 dose of 60 μg of nonadjuvanted RSV-PreF or Tdap. Results Both studies showed similar reactogenicity profiles for RSV-PreF and Tdap. No serious adverse events were considered vaccine related. In RSV F-020, geometric mean ratios of RSV-A neutralizing antibody levels at day 30 versus prevaccination were 3.1-3.9 in RSV-PreF recipients and 0.9 in controls. Palivizumab-competing antibody concentrations increased >14-fold in RSV-PreF recipients on day 30. RSV antibody titers waned after day 30 but remained well above baseline through day 90. Conclusions All formulations of RSV-PreF boosted preexisting immune responses in 18-45-year old women with comparable immunogenicity. The RSV-PreF safety profile was similar to that of Tdap vaccine.