PRELICENSING STUDIES with the experimental live-virus chickenpox vaccine had been going well. The manufacturer, Merck Sharp & Dohme, West Point, Pa, decided to start making the vaccine in quantity.
The first production lots of any new unlicensed vaccine also are for investigational use, including testing in additional human trials. At this point, a problem emerged. In the volunteers with leukemia who were given this production vaccine, there were more frequent vesicular lesions when compared with patients with leukemia who had received the research vaccine. The difference was statistically significant.
Even though there was no increase in adverse effects in normal subjects and no serious reactions occurred even in subjects with leukemia, Merck stopped trials with the vaccine while the problem was investigated. That was in January 1986.
Almost 18 months later, after extensive review of all the clinical data and of the steps involved in making both the earlier research