A bovine parainfluenza virus type 3 vaccine is safe and immunogenic in early infancy

Background. A phase 2 trial was conducted to assess in young infants the safety, tolerability, infectivity, and immunogenicity of multiple doses of an intranasal vaccine using bovine parainfluenza virus type 3 (bPIV3). Methods. One hundred ninety-two healthy 2-month-old infants were randomized 1: 1: 1 to receive 1 x 10(5) median tissue culture infective dose (TCID50) bPIV3 vaccine, 1 x 10(6) TCID50 bPIV3 vaccine, or placebo at 2, 4, 6, and 12 - 15 months of age. Safety information was collected by use of diary sheets and telephone interviews. Nasal wash and serum specimens were collected for assessment of infectivity and immunogenicity. Results. The safety profiles of both dosages of bPIV3 were similar to that of placebo, with the exception of fever with temperature of greater than or equal to 38.1 degreesC after dose 2 only, occurring in 34% of the 1 x 10(5) TCID50 group, 35% of the 1 x 10(6) TCID50 group, and 12% of the placebo group (P < .01). No vaccine-related serious adverse events were reported. The cumulative vaccine infectivity ( isolation of bPIV3 and/or bPIV3 seroconversion) after dose 3 was similar in the 2 vaccine groups (87% in the 1 x 10(5) TCID50 group and 77% in the 1 x 10(6) TCID50 group) (P = .46). Seroconversion rates after dose 3, assessed by means of hemagglutination inhibition assay, after adjustment for decrease in maternal antibody titers, were 67% in the 1 x 10(5) TCID50 group, 57% in the 1 x 10(6) TCID50 group, and 12% in the placebo group (P < .01). Isolation of bPIV3 was common after dose 1, dose 2, or dose 3, but only 1 of 51 participants in the vaccine groups had bPIV3 isolated after dose 4. Conclusions. Multiple doses of bPIV3 vaccine were well tolerated and immunogenic in young infants.