Thirty-five years of leaky vaccines.

Over the past 35 years, the term "leaky vaccine" has gained widespread use in both mathematical modeling and epidemiologic methods for evaluating vaccines. Here, we present a short history, as we recall it, of how the term was coined in the context of the history of sporozoite malaria vaccines that were thought in the 1980s to be possibly leaky. We draw a contrast with the all-or-none vaccine mechanism and review a few consequences for study design and population-level effects. We invite readers to contribute information covering the period preceding our memories in the 1980s, because we may have overlooked something.