Study: More Than 1 in 6 Toddlers Do Not Complete Childhood Vaccine Series


Pharmacists can play a crucial role in educating parents and helping remind them about the childhood vaccine schedule, which can be quite complex.

New study findings published in Pediatrics show that many young children initiate but do not finish their early childhood vaccine series.1

Image credit: anon |

Image credit: anon |

Most of these vaccines require 3 to 4 doses for optimal protection, which appears to be a factor in why early childhood vaccine coverage remains below optimal levels. Failing to complete these series, however, leaves the children and their communities vulnerable to disease outbreaks and more severe illness.1

The combined 7-vaccine series protects toddlers from diphtheria, tetanus, and acellular pertussis (DTaP); pneumococcal infections; Haemophilus influenzae type b; hepatitis B; polio; measles; mumps; rubella; and varicella.1 In the study, investigators used 2019 National Immunization Survey-Child data to classify children aged 19 to 35 months into 1 of 3 vaccination patterns: completed the combined 7-vaccine series; did not initiate ≥1 of the 7-vaccine series; or initiated all series but did not complete ≥1 multidose series.2

Among 16,365 children, the investigators found that 72.9% completed the combined 7-vaccine series, 9.9% did not initiate ≥1 series, and 17.2% initiated but did not complete ≥1 multidose series. Approximately 8.4% of children needed only 1 additional vaccine dose from 1 of the 5 multidose series to complete the combined 7-vaccine series.2

The strongest associations with starting but not completing multidose vaccine series were moving across state lines, lack of insurance coverage, and having a greater number of children in the household. Houses that had 2 to 3 children had an adjusted prevalence ratio (aPR) of 1.29, whereas houses with 4 or more had an aPR of 1.68.2

Despite these mixed findings, the study did note that the percentage of toddlers who have received the recommended doses has increased over the past decade from 68.4% in 2012 (the Healthy People 2020 baseline) to 72.9% in 2019.3 Additionally, 4 vaccines in the series had coverage exceeding the Healthy People 2020 initiative’s 90% target, with polio the highest at 92.3%.

Although the coverage rates for the remaining 3 vaccines (DTaP, Haemophilus influenzae type b, and pneumococcal disease) did not meet the Healthy People 2020 targets, they were all slightly higher than the baseline.3

Based on these findings, the investigators said more than 1 in 6 children in the United States have initiated but not completed all doses in a multidose vaccine series, suggesting that there are significant structural barriers to vaccination. Increasing focus on strategies to encourage multidose series completion could help optimize protection from preventable diseases and achieve national goals for vaccination coverage.2

Pharmacists can play a crucial role in educating parents and helping remind them about the childhood vaccine schedule, which can be quite complex.


  1. More Than 1 in 6 Toddlers Don’t Complete Early Childhood Vaccine Series. News release. American Academy of Pediatrics. July 25, 2023. Accessed August 31, 2023.
  2. Michels SY, Niccolai LM, Hadler JL, Freeman RE, et al. Failure to Complete Multidose Vaccine Series in Early Childhood. Pediatrics. 2023;152(2). doi:10.1542/peds.2022-059844
  3. Study Finds Mixed Results on Early Childhood Vaccination. American Academy of Family Physicians. August 30, 2023. Accessed August 31, 2023.
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