Safety and Immunogenicity of the RSV-F Vaccine in Older Adults Previously Treated With the Same Vaccine or Placebo in the Prior Year.

A Phase II Randomized, Observer-Blind, Placebo-Controlled Study to Evaluate the Immunogenicity and Safety of a Respiratory Syncytial Virus (RSV) Recombinant F Nanoparticle Vaccine in Healthy Older Adult Subjects Previously Treated With the Same Vaccine, or Placebo, in the Prior Year; and to Estimate the Incidence Rate of RSV Disease and Vaccine Efficacy in Subjects Based on Their RSV F Vaccine Experience Over Two Consecutive Years.