HUMAN SCHISTOSOMIASIS - POTENTIAL CONSEQUENCES OF VACCINATION

The potential outcomes of a Phase II schistosomiasis vaccine trial are explored using mathematical models which assume some natural immunity and a vaccine providing partial protection for a limited time. Analys es suggest that vaccination may have only a limited impact on life-lon g cumulative worm burdens and may lead to increased susceptibility and higher worm burdens at some ages, a ''rebound'' effect which results from reduced opportunity to acquire natural immunity. There is a trade -off between the degree and duration of vaccine-induced protection; lo ng-lived vaccines may be preferable to vaccines giving greater protect ion but for a shorter time.