An age-stratified mathematical model to inform optimal measles vaccination strategies

Measles remains a significant global public health threat despite the availability of an effective vaccine. WHO recommends the first measles vaccine dose at 9-12 months of age, balancing maternal antibody interference and immune system maturity. However, infants younger than 9 months remain highly vulnerable, especially in regions with high transmission and low herd immunity. This study introduces an age-stratified, multi-compartmental model of measles transmission that captures infections in unvaccinated infants by explicitly modelling maternal immunity decay and early infection risks. The model's positivity is proven, and an analytical expression for the instantaneous replacement number is derived. For a non-age-stratified version, equilibrium points and their stability are analyzed. Using a bootstrap algorithm, critical parameters and age-specific transmission rates are identified by fitting the model to yearly incidence data from six measles-prevalent countries. The proposed model provides a framework for evaluating hypothetical vaccination scenarios, including different routine and supplementary dose schedules. Under the model assumptions, scenarios including MCV0 produced larger reductions in projected measles incidence than those without MCV0. The study estimates the relative number of cases averted and projects elimination timelines for several hypothetical scenarios, highlighting that combining routine and supplementary immunizations with alternative assumptions such as early measles vaccination may be highly effective.