Background: Immunizations represent a critical component of contemporary preventive measures. Their primary function is to safeguard against the development of diseases and the ensuing complications. Objective: The objective of this study is to evaluate the effects of the measles, mumps, and rubella immunization program on the population of children in Poland from 2014 to 2021. Material and methods: The vaccination rate against measles, mumps and rubella in the population aged 1–19 years was calculated. The numerator was the number of children vaccinated in a given year and the denominator was the number of children born in a given year. The rate of missed vaccinations was calculated, where the numerator was the difference between the number of children born in a given year and the number of children vaccinated in a given year, and the denominator was the number of children born in a given year. The incidence rate was calculated for the vaccinated and unvaccinated populations (per 1 million population). The numerator constituted the number of reported cases in a given calendar year, whilst the denominator represented the number of individuals in the vaccinated or unvaccinated population in an age group. Results: In the subsequent years a gradual decrease in vaccination coverage was observed among the youngest age groups: 1-year-olds (from 77.8% to 70.7%) and 2-year-olds (from 94.8% to 89.5%). In the population vaccinated against measles, the highest incidence of the disease was observed among 1-year-olds. A decline in the incidence of rubella can be observed in subsequent years, both in the vaccinated and unvaccinated populations. A lower incidence of diseases was observed in 2020 and 2021 in all age groups. Conclusions: A significant decrease in the incidence of measles, mumps and rubella has been observed between 2014-2021 in the vaccinated population in comparison to the unvaccinated population.