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A single dose of either 30 µg or 60 µg of nonadjuvanted respiratory syncytial virus prefusion F protein antigen boosts humoral immune responses in women of childbearing age. The investigational vaccine was well tolerated and had a safety profile similar to that of the widely used combined Tdap vaccine. Abstract 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.

Abstract Background Respiratory syncytial virus (RSV) is a common cause of respiratory tract illness and hospitalization in neonates and infants. RSV vaccination during pregnancy may protect offspring in their first months of life. Methods This randomized, observer-blind, multicenter, phase 2 study evaluated the immunogenicity and safety of an RSV candidate vaccine in healthy nonpregnant women aged 18–45 years. Four hundred participants were randomized (1:1:1:1) to receive a single intramuscular dose of vaccine containing 30 µg, 60 µg, or 120 µg of RSV fusion protein engineered to preferentially maintain a prefusion conformation (RSV-PreF vaccine) or placebo. Results Thirty days postvaccination, RSV-A neutralizing antibody geometric mean titers (GMTs) increased 3.75-, 4.42- and 4.36-fold; RSV-B neutralizing antibody GMTs 2.36-, 2.54- and 2.76-fold; and palivizumab competing antibody (PCA) concentrations 11.69-, 14.38- and 14.24-fold compared with baseline levels in the 30 µg, 60 µg, and 120 µg RSV-PreF groups, respectively. Antibody titers and PCA concentrations at day 30 were significantly higher with the 120 µg compared to the 30 µg RSV-PreF vaccine. All RSV-PreF vaccine formulations and the placebo had similar reactogenicity profiles. No serious adverse events were considered to be related to the RSV-PreF vaccine. Conclusions The 3 formulations of the investigational RSV-PreF vaccine were well-tolerated and induced RSV-A and RSV-B neutralizing antibodies and PCAs in healthy, nonpregnant women. Clinical Trials Registration NCT02956837. Three formulations of an investigational maternal respiratory syncytial virus (RSV) vaccine containing 30, 60, or 120 µg of antigen were well-tolerated and elicited a rise in RSV-A and RSV-B neutralizing antibody titers as well as palivizumab-competing antibody titers in healthy nonpregnant women.