Vaccination patterns and up-to-date status of children 19-35 months, 2011-2021.

Introduction: Being up-to-date with all recommended vaccines is needed to protect children from vaccine preventable diseases. Understanding vaccination patterns is needed to develop messaging and strategies to increase vaccination uptake and confidence.
Methods: Data from the 2011 to 2021 National Immunization Surveys was used to assess trends and disparities in vaccination patterns, zero vaccination status, and up-to-date status of U.S. children by 19-35 months.
Results: From 2011 to 2021, adherence to the recommended schedule using the stringent definition increased from 35.7 % to 52.2 % (p < 0.01), adherence to the alternate schedule decreased from 28.2 % to 15.1 % (p < 0.01), and proportion of children who were not up-to-date decreased from 49.0 % to 33.3 % (p < 0.01). However, the proportion of children who had zero vaccinations did not change from 2011 (0.9 %) to 2021 (0.9 %; p = 0.08). In 2021, children 19-23 months were less likely to follow the recommended schedule than children 24-29 months (49.2 % compared to 56.4 %, p < 0.01). Adherence to the recommended schedule among children 19-23 months decreased in 2021 compared to 2020 overall and for some subpopulations (e.g. those with non-Hispanic (NH) Black parents (33.2 % compared to 44.9 %, p < 0.01). Furthermore, it was lowest among children of NH Black parents living at or below the federal poverty level (31.2 %) compared to their respective NH White counterparts (43.6 %, p < 0.01).
Conclusions: While there were overall increases in adherence to the recommended schedule from 2011 to 2021, a sustained catch-up program is needed to prevent missed vaccinations and achieve equitable vaccination coverage for all children.
Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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