Birth Cohort Study on Longitudinal Impact of Internal Migration Status on Routine Vaccination Coverage in the First Three Years of Life - Beijing, China, 2021-2025.

WHAT IS ALREADY KNOWN ABOUT THIS TOPIC?: High population mobility frequently undermines public health efforts to maintain immunization coverage, as mobile families often face barriers to accessing consistent healthcare.

WHAT IS ADDED BY THIS REPORT?: Migration across provincial-level administrative divisions (PLADs) drives progressively widening coverage disparities while contributing to delayed vaccination and missed catch-up opportunities within the National Immunization Program (NIP) during the first three years of life in China.

WHAT ARE THE IMPLICATIONS FOR PUBLIC HEALTH PRACTICE?: These findings underscore the need for a dynamic, life-course approach to migrant child immunization, with heightened focus on ensuring coverage during infancy. Vaccination verification and catch-up efforts should be intensified at preschool enrollment.