Clinical and serologic testing of a live varicella vaccine and two-year follow-up for immunity of the vaccinated children.

A live varicella vaccine derived from the Oka strain was given on 181 children who had no history of varicella and were seronegative by complement fixation (CF) and neutralization (NT) tests; 125 children were hospitalized and 54 were receiving steroid therapy. Overall, seroconversion was achieved in 85.1% of the children by the CF test and in 97.8% by the NT test. Clinical reaction consisting of mild fever and rash appeared in only two children. One hundred seventy-nine of the vaccinated children were followed up by questionnaire and 51 were followed up serologically approximately two years later, at which time 10 of 51 (19.6%) were seropositive by the CF test and 50 of 51 (98.0%) by the NT test. Only one out of 80 children who had postvaccinal contact with varicella contracted mild varicella 16 months after vaccination. None of the vaccinees developed herpes zoster. These results suggest that this live varicella vaccine may safely and effectively be used for children with or without underlying diseases, including those receiving steroid therapy, and that immunity of at least two years' duration is conferred upon the vaccinated subjects.