Biologic and geographic differences between vaccine and clinical varicella-zoster virus isolates.

Vaccine and wild-type strains of varicella-zoster virus differ both in their biologic characteristics and in the clinical manifestations of infection caused by each strain. The biologic differences described for the vaccine strain (temperature sensitivity and host cell preference) probably reflect the methods used to adapt the wild-type strain to the in vitro growth conditions imposed during the attenuation process in cell culture. In addition, restriction fragment polymorphisms have been described that reflect geographic strain variations between the parental virus used to develop the vaccine strain and other wild-type strains. These polymorphisms have been exploited as tools for the identification and differentiation of vaccine and wild-type strains in clinical studies. Infection with the wild-type strain results in the typical extensive rash of varicella, frequent transmission to other susceptible contacts, establishment of latency, and in some individuals, reactivation with the clinical picture of zoster. Infection with the vaccine strain results in the development of a protective immune response, minimal rash in a minority of individuals, rare transmission to other susceptible contacts, and a greatly reduced risk of zoster.