Adherence to Timely Vaccinations in the United States

To estimate (1) the proportion of children not adhering to the Advisory Committee on Immunization Practices (ACIP) recommended early childhood immunization schedule and (2) associations between schedule adherence, sociodemographic characteristics, and up-to-date immunization status by 19 to 35 months of age.

We used 2014 National Immunization Survey provider-verified vaccination data to classify vaccination patterns as "recommended" (ie, in line with ACIP dose- and age-specific recommendations), "alternate" (ie, in line with either limiting the number of shots per visit or skipping at least 1 vaccine series), or "unknown or unclassifiable" (ie, not in line with ACIP recommendations or clearly limiting shots per visit or vaccine series). We evaluated the association between vaccination patterns and up-to-date status for all ACIP-recommended vaccinations (including rotavirus and hepatitis A vaccines) using Poisson regression.

The majority of children's patterns were classified as "recommended" (63%), with 23% and 14% following alternate or unknown or unclassifiable patterns, respectively; 58% of children were up-to-date with all ACIP-recommended immunizations by 19 to 35 months. Not being up-to-date was associated with alternate (prevalence ratio = 4.2, 95% confidence interval: 3.9-4.5) and unknown or unclassifiable (prevalence ratio = 2.4, 95% confidence interval: 2.2-2.7) patterns.

High vaccine coverage by 19 to 35 months of age may miss nonadherence to the recommended immunization schedule in the first 18 months of life, leaving children vulnerable to preventable diseases. With more than one-third of US children not following the ACIP schedule, targeted interventions are needed to minimize vaccine delays and disease susceptibility.