Comparison of the immunogenicity and efficacy of a replication-defective vaccinia virus expressing antigens of human parainfluenza virus type 3 (HPIV3) with those of a live attenuated HPIV3 vaccine candidate in rhesus monkeys passively immunized with PIV3 antibodies

Two parainfluenza virus type 3 (PIV3) vaccine candidates-cp45, a live atten uated derivative of the JS wild type (wt), and a replication-defective vacc inia virus recombinant expressing the hemagglutinin-neuraminidase or fusion glycoprotein of human PIV3 (modified vaccinia virus Ankara [MVA]/PIV3 reco mbinants)-were evaluated in rhesus monkeys to determine whether successful immunization could be achieved in the presence of passively transferred PIV 3 antibodies. The cp45 virus, administered intranasally (in) and intratrach eally (it) in the presence of high levels of PIV3 antibodies, replicated ef ficiently in the nasopharynx and protected against challenge with wt human PIV3, The MVA recombinants, administered in, it, and intramuscularly in the absence of passive antibody, conferred protection against replication of P IV3 wt challenge virus, but this was largely abrogated when immunization oc curred in the presence of passive antibodies. Because immunization for the prevention of HPIV3 disease must occur in early infancy when maternal antib odies are present, the live attenuated cp45 virus continues to be a promisi ng vaccine candidate for this age group.