Invalid Vaccine Doses Among Children Aged 0 to 35 Months: 2011 to 2020

Vaccine doses provided outside the Advisory Committee on Immunization Practices for minimum and maximum ages of vaccination and minimum intervals between doses are considered invalid. Our objective was to quantify the prevalence of and factors associated with invalid doses among US children aged 0 to 35 months.

We analyzed provider-verified vaccination records from the nationally representative 2011-2020 National Immunization Survey-Child. We quantified the number of children with at least 1 invalid vaccine dose overall, by survey year, and by vaccine type. Among children who received vaccine doses before the minimum age or minimum dose interval, we quantified the prevalence of receiving extra doses such that series were completed with the recommended number of valid doses. We used logistic regression models to identify factors associated with receipt of an invalid vaccination.

Of 161 187 children, 22 209 (weighted percent: 15.4%, 95% CI, 15.0%-15.8%) had an invalid vaccine dose. Of children with a minimum age or minimum interval invalid dose, 44.9% (95% CI, 43.2%-46.6%) received extra doses and completed the series. The highest prevalence of invalid doses was for 3-dose rotavirus (n = 5733, 4.4%), with the first dose being administered after the maximum age (n = 3996, 3.1%). Overall, the percentage of children with an invalid dose decreased from 2011 (16.9%) to 2020 (12.5%). Children who moved across state lines vs not (adjusted odds ratio: 1.5 [95% CI, 1.4-1.6]) had higher odds of an invalid vaccine dose.

Although invalid vaccine doses have decreased over time, many children with invalid doses lacked the doses necessary to complete a vaccine series.