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Methods

Without vaccination, measles is a highly contagious disease; estimates of the basic reproductive number (R 0) from the prevaccination era range from 11 to 18. 3 R 0 is the mean number of secondary infections per infectious agent that occurs during the course of the entire infectious period in a population that is 100% susceptible at time 0. 3 However, when a portion of the population is immune to a given disease, effective reproductive number (R E) is observed instead of R 0. 3 When historical values of R 0 are available and R E can be approximated, the rate of immunity in the exposed population can be estimated. 3 Furthermore, in situations where immunity is primarily conferred via vaccination, rate of immunity (I) and rate of vaccination effectiveness (V E) can be used to estimate rate of vaccination (V) in the exposed population as follows: