Vaccine-induced immunity did not wane in the reference scenario. When a slow waning was included (from our previous study www.thelancet.com/journals/lan...), the impact of early MMR2 delivery decreased slightly (5.28% reduction). If waning started at a younger age, the reduction dropped to 3.79%.

The different vaccination strategies changed the age distribution of the cases: an earlier delivery of MMR2 led to a lower proportion of measles cases in children aged between 2 and 4. A 0.5% increase of MMR1 uptake decreased the number of measles cases across all age groups.

We used a compartmental model stratified by age and region, and simulated outbreaks with different vaccination schedules and coverage. Without changes to coverage, moving MMR2 to 2 years reduced the number of cases by 11.86%, similar to increasing MMR1 coverage by 0.5% across all regions and years.