To the Editor.
—We welcome the vision of Dr de Quadros and colleagues1 in proposing a coordinated strategy for the elimination of measles from the Americas and would endorse their basic approach. However, while the combination of experience, common sense, and guesswork used to develop the strategy has so far proved successful, we would argue that the design is not optimal and that it would benefit from judicious use of the well-established theory of infectious disease transmission.2,3 This is particularly necessary if the strategy is to be adopted in other regions.Specifically, the criterion used to determine the time interval between follow-up campaigns should be revised. Their calculation is based on the assertion that when the number of susceptible children is equal to the number of children in 1 birth cohort it is "almost certainly" enough to permit an outbreak to occur. No evidence is provided to support