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)-cp45 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 wtHPIV3. Following vaccination viral cultures were obtained on nine occasions to detect shedding and transmission of HPIV3cp45. Serum antibody titers were measured before and 7 weeks after vaccination.
Results: No child fulfilled the criteria for transmission of HPIV3cp45 giving a risk of transmission of 0.04 (95% CI 0.01-0.19), hence establishing that HPIV3cp45 is less infectious than wtHPIV3 and risk of transmission is not a limitation to further clinical development of this vaccine candidate.