Reported Vaccination Coverage and Model-Implied Measles Susceptibility in Kazakhstan, 2019-2026

Background. Kazakhstan recorded 29,731 confirmed measles cases in 2023 and 28,147 in 2024, while declared first-dose vaccination coverage averaged 95.6 percent in 2019-2022. This study uses official monthly data and simple mathematical models to estimate how many people were susceptible to measles before the outbreak and what vaccination coverage the country needs. Methods. Monthly data on confirmed cases, vaccination coverage and the vaccination status of cases for 20 regions, January 2019 to July 2026, were obtained from the Ministry of Health of the Republic of Kazakhstan through a formal information request. The susceptible share before the 2023-2024 wave was estimated with the final size equation of the SIR model and, independently, from the early growth rate of the outbreak. Required coverage was computed as (1 - 1/R0)/E, where R0 is the basic reproduction number and E is vaccine efficacy. The hypothesis and its threshold were fixed in a written protocol before the analysis. Results. The 2023-2024 wave contained 57,587 cases and peaked at 10,016 cases in December 2023. At R0 = 12, the susceptible share before the wave was 8.5-8.8 percent by the final size method and 11.4-12.1 percent by the growth-rate method, against 4.4 percent implied by declared coverage. The difference exceeded 2 percentage points for every R0 from 8 to 16. With a two-dose efficacy of 0.97, the 95 percent coverage target is sufficient only for R0 up to 12. In 2025 and January-July 2026, 74-78 percent of cases were unvaccinated, refusal was the most common reason, and people with two doses made up 3.1-3.5 percent of cases. Conclusions. Two independent methods show that more people were susceptible to measles before the 2023-2024 outbreak than declared coverage implies. Most recent cases occurred among unvaccinated people. A simple accumulation model forecasts that the number of susceptible people returns to the epidemic threshold between October 2026 and November 2029.