IMPERFECT VACCINES AND HERD-IMMUNITY TO HIV

A number of prophylactic vaccines against human immunodeficiency virus (HIV) have passed through phase I clinical trials, and phase II clini cal trials are now being planned. These vaccines are not expected to b e perfect and might fail in a number of different ways. This paper sho ws how to equate different aspects of imperfection in a prophylactic v accine in terms of impact upon levels of herd immunity, and hence upon the vaccine coverage required for eradication. Such comparisons revea l that an otherwise perfect vaccine that gives protection which wanes with a half-life of 10 years is only as good as a vaccine that works i n 30% of people giving them complete, lifelong protection. The paper g oes on to compare predicted patterns of seroconversion that would be o bserved in clinical trials and in community-wide vaccination campaigns for vaccines that confer the same levels of herd immunity but are imp erfect in different ways.