Modelling the influence of changes in vaccination timing, timeliness and coverage on the example of measles outbreaks in the UK between 2010-19

BackgroundThe Measles-Mumps-Rubella vaccine is given as a two-dose course in childhood, but the schedule of the second dose varies between countries. England recommended bringing forward the second dose from three years and four months to 18 months by 2025. We aim to quantify how changing the vaccine schedule could impact measles transmission dynamics. MethodsWe used a mathematical model stratified by age group and region to generate stochastic outbreaks with different vaccine schedules. We used detailed information on vaccine uptake for different age groups by region and year from electronic health records and modelled alternative scenarios changing the timing of the second MMR dose or changing uptake of either dose. We simulated measles incidence between 2010 and 2019 and compared the number of cases in each scenario. Results and discussionDelivering the second MMR vaccine at younger age resulted in a lower number of cases than in the reference set of simulations with 16% (IQR: 1.93- 28.48%) cases averted when the second dose was given at 18 months. The number of cases decreased even if the coverage of the second dose decreased by up to 3% (median reduction 15.94%; IQR: 0.41 -28.21%). The impact on case numbers was equivalent to increasing first dose coverage by 0.5% every year between 2010 and 2019 (16.38 % reduction, IQR:1.90 - 28.45), more cases could be avoided (28.60%, IQR: 17.08 - 38.05) if the first dose coverage was increased by 1% every year. Our data highlighted how patterns of vaccination uptake translate into outbreak risk. Although increasing coverage of the first MMR dose led to the best results, this may be challenging to achieve requiring substantial resources with already high coverage of the first dose. Hence, an earlier second MMR dose presents a good alternative for mitigating the risk of measles outbreaks.