Clinical and Laboratory Studies of KMcC Strain Live Attenuated Varicella Virus

Abstract Small-scale studies were carried out to test the KMcC strain varicella virus at various passage levels for clinical and serologic responses in order to find an optimal level of attenuation for vaccine purpose. Virus at passage 50 induced antibody responses, caused only minimal clinical reactions, and will be studied further. The clinical reactions to vaccine virus were very mild at all virus passage levels and were limited to mild transient fever and papular rash that became vesicular in a small proportion of individuals. The immune response to vaccination was accompanied by protection against natural challenge and antibody induced by vaccine virus persisted for at least 3.5 years, the longest period observed. Attenuation of virus appeared to be accompanied by alteration in the proportion of incomplete virus particles formed and by the degree of spontaneous release of virus from infected cells.