Transmissibility, infectivity and immunogenicity of a live human parainfluenza type 3 virus vaccine (HPIV3cp45) among susceptible infants and toddlers

Background This study examined the transmissibility between young children of an intranasally administered live attenuated human parainfluenza virus type 3 (HPIV3)- cp 45 vaccine candidate. Methods Eighty subjects were enrolled in playgroups among whom there was at least one infected vaccinee in close contact with a seronegative placebo recipient over 21 days without a confounding infection with wt HPIV3. Following vaccination viral cultures were obtained on nine occasions to detect shedding and transmission of HPIV3 cp 45. Serum antibody titers were measured before and 7 weeks after vaccination. Results No child fulfilled the criteria for transmission of HPIV3 cp 45 giving a risk of transmission of 0.04 (95% CI 0.01–0.19), hence establishing that HPIV3 cp 45 is less infectious than wt HPIV3 and risk of transmission is not a limitation to further clinical development of this vaccine candidate.