Nineteen (22·9%) of 83 sera collected before vaccination from adult volunteers aged 21–64 years were without neutralizing antibody to poliomyeitis at levels of 0·15 i.u./ml for types I and II and 0·1 i.u./ml for type III. Some correlations were found between the history of previous vaccination and the presence of antibody but these were not well defined.
Vaccination with a single dose of trivalent oral polio vaccine elicited fourfold or greater antibody responses to one or more poliomyelitis types in 53 (63·9%) volunteers, the percentage antibody responses being inversely related to the titre of antibody present before vaccination. Types I, II or III poliomyelitis virus were recovered from 76·8 % of faecal samples collected 1 week after vaccination. The percentage recovery progressively declined thereafter until virus was recovered from 10·5 % of samples collected 6 weeks after vaccination.
Type for type, the titres and percentages of antibody responses and virus shedding in faeces were similar following trivalent oral poliomyelitis vaccines whether prepared in monkey kidney or human diploid cell substrates. Some change in reproductive capacity temperature (r.c.t./40) marker was found in faecal isolates from volunteers vaccinated with monkey kidney and human diploid grown vaccines but no change in ‘d’ marker was found.