Characterizing timeliness of recommended vaccinations among privately-insured children in the United States, 2009–2019

Background: The Advisory Committee on Immunization Practices (ACIP) recommends early childhood vaccinations, but knowledge is limited about the magnitude and timing of vaccine delay for each recommended dose on a population level. We sought to characterize longitudinal patient-level patterns of early childhood vaccination schedule adherence. Methods: Using the Merative MarketScan Commercial Database (2009–2019), we identified commercially-insured infants who received at least one timely dose of a 2-month recommended vaccine. We categorized the number of recommended vaccines administered on the same date at 2, 4, 6, and 12–15 months of age (grace period: −7, +21 days). A Sankey diagram illustrated the number of vaccines received concomitantly during each age window and depicted transitions to different states over time (e.g., no vaccine delay to vaccine delay). For each vaccine dose, we estimated the cumulative incidence of receipt. Results: Among 1,239,364 eligible children, 28% of infants aged 4 months and 38% of infants aged 6 months did not receive timely, concomitant administration of all recommended vaccines. The number of timely vaccines received concomitantly and age at receipt varied most for doses recommended during the second year of life. Children with a previously delayed (versus timely) dose consistently experienced longer time to subsequent dose. Conclusions: National coverage improved over time for all recommended vaccine doses under study, most notably for measles, mumps, and rubella. However, many children do not receive vaccines on schedule. Interventions to maintain adherence to the recommended schedule are needed early in life.