Phase 2 Evaluation of Parainfluenza Type 3 Cold Passage Mutant 45 Live Attenuated Vaccine in Healthy Children 6–18 Months Old

A phase 2 evaluation of live attenuated parainfluenza type 3 (PIV3)-cold passage mutant 45 (cp45) vaccine was conducted in 380 children 6-18 months old; 226 children (59%) were seronegative for PIV3. Of the 226 seronegative children, 114 received PIV3-cp45 vaccine, and 112 received placebo. No significant difference in the occurrence of adverse events (i.e., runny nose, cough, or temperature > or =38 degrees C) was noted during the 14 days after vaccination. There was no difference between groups in the occurrence of acute otitis media or serous otitis media. Paired serum samples were available for 109 of the seronegative vaccine recipients and for 110 of the seronegative placebo recipients; 84% of seronegative vaccine recipients developed a > or =4-fold increase in antibody titers. The geometric mean antibody titer after vaccination was 1 : 25 in the vaccine group and <1 : 4 in the placebo group. PIV3-cp45 vaccine was safe and immunogenic in seronegative children and should be evaluated for efficacy in a phase 3 field trial.