Authors' reply

摘要

In response to Suman Saurabh and Ritesh Kumar, although the rate of infection shares some features of SIR models, our aim was to use a flexible formulation that reproduced the key features of an SIR-type model. Specifically, the infection rate should scale positively with the proportion of the population that is susceptible. As correctly noted, we assume that the force of infection is constant throughout the year, although standard SIR formulations suggest the force of infection should change through time as S/N and I fluctuate. We are presently unable to go beyond annual approximations because the available data are annualised and because the seasonal fluctuations in measles transmission rates have not been characterised for most countries.