A LIVE HUMAN PARAINFLUENZA TYPE-3 VIRUS-VACCINE IS ATTENUATED AND IMMUNOGENIC IN HEALTHY INFANTS AND CHILDREN

The safety, infectivity, immunogenicity, and phenotypic stability of t he cold-passaged (cp) candidate vaccine cp-45, a cold-adapted (ca), te mperature-sensitive (ts) mutant of the JS strain of human parainfluenz a virus type 3 (HPIV-3), was evaluated in 114 children 6 months to 10 years old in a randomized, placebo-controlled, double-blind trial. The cp-45 vaccine was well tolerated when given intranasally to parainflu enza virus type 3 (PIV-3)-seropositive and -seronegative children. Wit h 10(4) or 10(5) TCID50 of cp-45 vaccine, 86% of seronegative vaccinee s were infected, 83% of whom shed virus at a mean peak titer of 10(2.2 ) pfu/ml. Virus present in respiratory specimens retained the ts pheno type, and each of 86 PIV-3 isolates tested retained both the ca and ts phenotypes. One dose of 10(5) TCID50 of vaccine induced a serum hemag glutination-inhibiting antibody response in 81% of vaccinees; the geom etric mean titer was 1:32. These studies indicate that the cp-45 HPIV- 3 vaccine is satisfactorily attenuated, infectious, immunogenic, and p henotypically stable and merits further evaluation in infants and youn g children.