Search

Background Protection against human respiratory syncytial virus (RSV) remains an unmet need potentially addressable by maternal immunization. This phase 1/2 study evaluated a bivalent prefusion F vaccine (RSVpreF) with antigens from RSV subgroups A and B. Methods Adults 18–49 years old (N = 618) were randomized to receive placebo or 60, 120, or 240 µg RSVpreF with or without Al(OH)3. Safety and immunogenicity were evaluated. Results RSVpreF recipients more frequently reported local reactions and systemic events than placebo recipients; these were mostly mild or moderate. No vaccine-related serious adverse events occurred through 12 months postvaccination. All RSVpreF formulations induced 1-month postvaccination virus-neutralizing titers higher than those associated with protection of high-risk infants by palivizumab, the only prophylactic currently available for RSV. Geometric mean fold rises (GMFRs) across RSVpreF doses/formulations were 10.6–16.9 for RSV A and 10.3–19.8 for RSV B at 1 month postvaccination, greater than those historically elicited by postfusion F vaccines. GMFRs were 3.9–5.2 and 3.7–5.1, respectively, at 12 months postvaccination. Conclusions RSVpreF formulations were safe, well tolerated, and induced robust neutralizing responses in adults. These findings support development of RSVpreF, which is being evaluated in a pivotal phase 3 study for maternal immunization. Clinical Trials Registration NCT03529773.

Although human respiratory syncytial virus (RSV) is an important cause of illness and death in older adults, no RSV vaccine has been licensed.In a phase 2a study, we randomly assigned healthy adults (18 to 50 years of age), in a 1:1 ratio, to receive a single intramuscular injection of either bivalent prefusion F (RSVpreF) vaccine or placebo. Approximately 28 days after injection, participants were inoculated intranasally with the RSV A Memphis 37b challenge virus and observed for 12 days. The per-protocol prespecified primary end points were the following: reverse-transcriptase-quantitative polymerase-chain-reaction (RT-qPCR)-confirmed detectable RSV infection on at least 2 consecutive days with at least one clinical symptom of any grade from two categories or at least one grade 2 symptom from any category, the total symptom score from day 1 to discharge, and the area under the curve (AUC) for the RSV viral load in nasal-wash samples measured by means of RT-qPCR from day 2 after challenge to discharge. In addition, we assessed immunogenicity and safety.After participants were inoculated with the challenge virus, vaccine efficacy of 86.7% (95% CI, 53.8 to 96.5) was observed for symptomatic RSV infection confirmed by any detectable viral RNA on at least 2 consecutive days. The median AUC for the RSV viral load (hours × logRSVpreF vaccine was effective against symptomatic RSV infection and viral shedding. No evident safety concerns were identified. These findings provide support for further evaluation of RSVpreF vaccine in a phase 3 efficacy study. (Funded by Pfizer; EudraCT number, 2020-003887-21; ClinicalTrials.gov number, NCT04785612.).

BackgroundPrevention of respiratory syncytial virus (RSV) disease in infants is an unmet vaccine need, and maternal immunization is a potential strategy to address this need. This study evaluated concomitant administration of RSV stabilized prefusion F subunit vaccine (RSVpreF) and tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis vaccine adsorbed (Tdap) in healthy, nonpregnant women 18‒49 years of age.MethodsIn this phase 2b, multicenter, placebo-controlled, observer-blind, noninferiority study, participants were randomized to receive RSVpreF in a range of doses and formulations with Tdap or alone, or Tdap alone. Safety and immunogenicity were assessed.ResultsLocal reactions and systemic events were generally similar across vaccine groups. Noninferiority of anti-RSV-A and anti-RSV-B immune responses induced by RSVpreF with Tdap was demonstrated compared to RSVpreF alone. Noninferiority of anti-diphtheria toxoid and anti-tetanus toxoid immune responses after administration of RSVpreF with Tdap was demonstrated compared to Tdap alone; noninferiority was not met for anti-pertussis component responses.ConclusionsRSVpreF was safe and well tolerated when administered with Tdap or alone in nonpregnant women 18‒49 years of age. Immune responses induced by Tdap administered with RSVpreF were noninferior for the tetanus and diphtheria components of Tdap, but not for pertussis.Clinical Trials RegistrationNCT04071158.

Background The respiratory syncytial virus (RSV) fusion glycoprotein (F) is a molecule that fuses the viral and host cell membranes during virus entry as it rearranges from a meta-stable prefusion to a stable postfusion conformation. Using structure-guided design, Pfizer engineered a prefusion RSV F subunit vaccine antigen with stable and well-characterized conformational homogeneity. Methods We report results of a 1,182 subject, first-in-human, phase 1/2, placebo-controlled, randomized, observer-blind, dose-finding study to describe the safety, tolerability, and immunogenicity of the Pfizer RSV vaccine candidate in healthy men and non-pregnant women from 18 to 85 years of age. The study compares three dosages of the vaccine candidate, with and without aluminum hydroxide, and also compares immunization with the RSV vaccine candidate alone or concomitantly with influenza vaccine. The study is ongoing to collect antibody persistence and additional safety data. Results The data, which are currently available for the 18- to 49-year-old subgroup, demonstrate an excellent safety and tolerability profile. Immunization with the various formulations of the vaccine candidate elicited RSV 50% neutralization titer geometric mean fold rises (GMFRs) of 10.6–17.2 for subgroup A and 10.4–19.8 for subgroup B, measured one month after immunization, with evidence of a dose–response. Conclusion The 10- to 20-fold increases in neutralizing antibody titers elicited by this vaccine with a stable prefusion F antigen represent a step change relative to the historical performance of vaccine candidates, such as Wyeth’s PFP, with F antigens that were not stabilized in the prefusion conformation (Simoes et al., Vaccine 20:954–60, 2002). The data strongly support development of this vaccine candidate to prevent RSV disease in infants, by immunizing pregnant women, and to prevent RSV disease in older adults, by direct immunization. Disclosures All authors: No reported disclosures.