Vaccination Timeliness Among US Children Aged 0-19 Months, National Immunization Survey-Child 2011-2021

Abstract

Importance: Delays in receiving vaccinations lead to greater vaccine-preventable disease risk. Timeliness of receipt of recommended vaccinations is not routinely tracked in the US, either overall or for populations that have known barriers to accessing routine health care, including lower-income families and children.

Objective: To measure vaccination timeliness among US children aged 0 to 19 months, overall and by socioeconomic indicators.

Design, setting, and participants: This serial, cross-sectional study analyzed nationally representative data from the 2011 to 2021 National Immunization Survey-Child (NIS-Child), an annual survey of parents, with immunization histories collected from clinicians administering vaccines. The 2020 and 2021 surveys largely reflected vaccinations in the US before the COVID-19 pandemic. Study participants included US children surveyed at ages 19 to 35 months. Data were analyzed from January to August 2023.

Exposure: Survey year.

Main outcomes and measures: The primary outcomes were average days undervaccinated (ADU) and percentage of children who received all vaccine doses on time (ie, 0 days undervaccinated) for the combined 7-vaccine series up to age 19 months. The mean adjusted annual change in on-time vaccination by socioeconomic indicators was calculated by use of multivariable log-linked binomial regression models.

Results: The surveys included 179 154 children (92 248 boys [51.2%]); 74 479 (31.4%, weighted) lived above the federal poverty level with more than $75 000 in annual family income, 58 961 (32.4%) lived at or above the poverty level with $75 000 or less in annual family income, and 39 564 (30.2%) lived below the poverty level. Overall, the median (IQR) ADU for the combined 7-vaccine series in the US decreased from 22.3 (0.4-71.5) days in the 2011 survey to 11.9 (0.0-55.5) days in the 2021 survey. The prevalence of on-time receipt of the combined 7-vaccine series increased from 22.5% (95% CI, 21.4%-23.6%) to 35.6% (95% CI, 34.2%-37.0%). Although children with more than $75 000 in annual family income had a 4.6% (95% CI, 4.0%-5.2%) mean annual increase in on-time vaccination, the mean annual increase was 2.8% (95% CI, 2.0%-3.6%) for children living at or above the poverty level with $75 000 or less in annual family income and 2.0% (95% CI, 1.0%-3.0%) for children living below the poverty level.

Conclusions and relevance: In this cross-sectional study of NIS-Child data, improvements in vaccination timeliness were observed from the 2011 to the 2021 survey. However, widening disparities by socioeconomic indicators signal that increased efforts to facilitate timely vaccination among children in lower-income families are needed.

Figure 1.. Prevalence of On-Time Receipt for 7 Vaccinations and for the Combined 7-Vaccine Series Among US Children Aged 0 to 19 Months, National Immunization Survey (NIS)–Child 2011-2021

On-time receipt is defined as 0 days undervaccinated. Significant changes in the prevalence of on-time vaccine receipt were observed for each vaccine series and for the combined 7-vaccine series (P < .001 for all). Statistical significance was assessed using log-linked binomial regression models with survey year as the independent variable to calculate the unadjusted mean annual change in the prevalence of on-time vaccine.

Figure 2.. Prevalence of On-Time Receipt for the Combined 7-Vaccine Series, by Poverty and Health Insurance Status

On-time receipt is defined as 0 days undervaccinated. A, Prevalence by poverty status based on US Census thresholds. Of the 179 154 US children with clinician-verified vaccination records in the 2011 to 2021 National Immunization Survey (NIS)–Child surveys, 6150 children were missing data on poverty status (6.0%, weighted). B, Prevalence by health insurance status. Among the total study sample, 4107 children were missing data on health insurance status (2.9%, weighted). If the child was enrolled in any form of Medicaid, alone or in combination with other types of health insurance coverage, the child was classified as any Medicaid in the NIS-Child survey. Other insurance includes the Children’s Health Insurance Program, Indian Health Service, Military, Tricare, Civilian Health and Medical Program of the Uniformed Services, or Civilian Health and Medical Program of the Department of Veterans Affairs (alone or in combination with private insurance).