Live attenuated varicella vaccine: immunization of healthy children with the OKA strain

Abstract

Ninety-one healthy children were immunized with one of three preparations of the OKA strain of live attenuated varicella zoster virus in order to gain sufficient information on safety and immunogenicity to justify vaccine studies in immunosuppressed children. The OKA-Biken vaccine was studied in a dose response trial. Two additional clinical trails were conducted with the OKA strain that was further passaged: a frozen aqueous (OKA-RIT-Aq) form and a lyophilized (OKA-RIT-Ly) form were tested. With each of these vaccines clinical reactivity was minimal and virus shedding, viremia, and transmission of the vaccine virus were absent. Excellent seroconversion rates of 100 and 94% were induced with approximately 500 pfu of OKA-Biken and OKA-RIT-Ly vaccine, respectively. A lower seroconversion rate was noted for OKA-RIT-Aq, presumably on the basis of defective individual vials. Diluted OKA-Biken vaccine induced less seroconversion but even the 5 pfu dose produced antibody responses in 81% of the vaccinees. In vitro specific cellular immune responses to varicella virus antigens were demonstrated in each group of vaccinees, including all but two of those vaccines who failed to seroconvert. The data indicate that two preparations of the OKA strain are sufficiently safe and immunogenic in healthy children to support further studies in immunocompromised children.