The Resurgence of Measles and Herd Immunity

Abstract

To the Editor. —Schlenker et al have documented evidence that immunization levels over 80% provided a significant level of herd immunity. 1 Their study also raises a question that was not addressed by the authors: what is the basis for the resurgence of measles in the preschool-age population? Although it is easy to assume that the resurgence is due to inadequate levels of vaccination, they estimated that the rates of immunization had not changed from 1982 through 1989. 1 Since there has been an increase in the number of births nationally, data were obtained from the Milwaukee (Wis) Public Health Department to determine whether there was any relation between the number of births and the measles epidemic. From 1980 through 1990, there was a 9% increase in the annual number of live births in the city of Milwaukee, from 11772 to 12780 (Gloria Tatum, Milwaukee Public Health Department, oral communication).