The cp-45 vaccine is appropriately attenuated and immunogenic in infants as young as 1 month of age. Further development of this vaccine is warranted.

Studies were initiated to define the genetic basis of the temperature-sensitive (ts), cold adaptation (ca), and attenuation (att) phenotypes of the human parainfluenza virus type 3 (PIV3) cp45 live attenuated vaccine candidate. Genetic data had previously suggested that the L polymerase protein of cp45, which contains three amino acid substitutions at positions 942, 992, and 1558, contributed to its temperature sensitivity (R. Ray, M. S. Galinski, B. R. Heminway, K. Meyer, F. K. Newman, and R. B. Belshe, J. Virol. 70:580–584, 1996; A. Stokes, E. L. Tierney, C. M. Sarris, B. R. Murphy, and S. L. Hall, Virus Res. 30:43–52, 1993). To study the individual and aggregate contributions that these amino acid substitutions make to the ts, att, and ca phenotypes of cp45, seven PIV3 recombinant viruses (three single, three double, and one triple mutant) representing all possible combinations of the three amino acid substitutions were recovered from full-length antigenomic cDNA and analyzed for their ts, att, and caphenotypes. None of the seven mutant recombinant PIVs was cold adapted. The substitutions at L protein amino acid positions 992 and 1558 each specified a 105-fold reduction in plaque formation in cell culture at 40°C, whereas the substitution at position 942 specified a 300-fold reduction. Thus, each of the three mutations contributes individually to the ts phenotype. The triple recombinant which possesses an L protein with all three mutations was almost as temperature sensitive as cp45, indicating that these mutations are the major contributors to the ts phenotype ofcp45. The three individual mutations in the L protein each contributed to restricted replication in the upper or lower respiratory tract of hamsters, and this likely contributes to the observed stability of the ts and att phenotypes ofcp45 during replication in vivo. Importantly, the recombinant virus possessing L protein with all three mutations was as restricted in replication as was the cp45 mutant in both the upper and lower respiratory tracts of hamsters, indicating that the L gene of the cp45 virus is a major attenuating component of this candidate vaccine.

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.

We evaluated a combination respiratory syncytial virus (RSV) and parainfluenza 3 virus (PIV3) live, attenuated intranasal vaccine for safety, viral replication, and immunogenicity in doubly seronegative children 6-18 months old. RSV cpts-248/404 and PIV3-cp45 vaccines were combined in a dose of 10(5) plaque-forming units of each per 0.5-mL dose and compared with monovalent vaccines or placebo. The virus shedding pattern of RSV was not different between monovalent RSV cpts-248/404 vaccine and combination vaccine. Modest reductions in the shedding of PIV3-cp45 vaccine virus were found after the administration of RSV cpts-248/404 and PIV3-cp45 vaccine, relative to monovalent PIV3 vaccine; 16 (76%) of 21 children given combination vaccine shed PIV3-cp45 versus 11 (92%) of 12 of those given monovalent PIV3 vaccine. Both vaccines were immunogenic, and antibody responses were similar between the monovalent groups and the combination group. Combined RSV/PV3 vaccine is feasible for simultaneous administration, and further studies are warranted.

The attenuated phenotype of Sabin 3 poliovirus compared with its neurovirulent progenitor strain has been largely accounted for by mutations in the genome at positions 472 and 2034 (G.