2ND-YEAR SURVEILLANCE OF RECIPIENTS OF A RESPIRATORY SYNCYTIAL VIRUS (RSV) F-PROTEIN SUBUNIT VACCINE, PFP-1 - EVALUATION OF ANTIBODY PERSISTENCE AND POSSIBLE DISEASE ENHANCEMENT

In a previous study, children 18 to 36 months of age and seropositive for respiratory syncytial virus (RSV) were vaccinated with an RSV subu nit vaccine (PFP-1) consisting of the viral fusion protein. Vaccinees developed substantial increases in anti-fusion and neutralizing antibo dy, and exhibited protection against RSV infection through one RSV epi demic, in comparison to controls. This present study of the same cohor t was undertaken to determine the persistence of antibody responses an d immunity to reinfection, as well as to monitor for enhanced disease upon subsequent RSV infection during the second RSV season after vacci nation. Vaccinees continued to have greater ELISA specific anti-fusion (F) antibody responses than controls up to 18 months after vaccinatio n. Neutralizing antibody, titres were not as durable, and the attack r ates for RSV in the second winter season after vaccination (25% in vac cinees versus 42% in controls) were not significantly different (p=0.2 3). Nevertheless, 'high-responder' subgroups may have had residual pro tection into the second postvaccination year. Enhanced illness did not occur. PFP-1 is immunogenic and appears safe, but yearly reimmunizati on may be necessary to maintain immunity to RSV infection.