Estimating the optimal age for infant measles vaccination

The persistence of measles in many regions demonstrates large immunity gaps, resulting from incomplete or ineffective immunization with measles-containing vaccines (MCVs). A key factor affecting MCV impact is age, with infants receiving dose 1 (MCV1) at older ages having a reduced risk of vaccine failure, but also an increased risk of contracting infection before vaccination. Here, we designed a new method—based on a transmission model incorporating realistic vaccination delays and age variations in MCV1 effectiveness—to capture this risk trade-off and estimate the optimal age for recommending MCV1. We predict a large heterogeneity in the optimal ages (range: 6–20 months), contrasting the homogeneity of observed recommendations worldwide. Furthermore, we show that the optimal age depends on the local epidemiology of measles, with a lower optimal age predicted in populations suffering higher transmission. Overall, our results suggest the scope for public health authorities to tailor the recommended schedule for better measles control.