Vaccination Estimates Could Overlook Delays

Measuring rates of vaccination coverage using up-to-date status at specific age ranges could overlook vaccination delays occurring earlier in life, according to the results of a recent study.

“Most vaccine coverage research is focused on the up-to-date status as reported by the CDC,” the authors of the study explained. These reports are based on whether the child received recommended vaccinations against 14 illnesses by age 19 to 35 months, and not on when the doses are given.

“[A]nalyses that are focused on up-to-date status at a specific age range (eg, 19–35 months of age) may miss vaccination delays early in life, when children may be unnecessarily at risk for disease. Although studies have evaluated early variation in vaccine schedule adherence in specific states, those findings alone lack generalizability to the United States as a whole,” they wrote.

They used data from the 2014 National Immunization Survey (NIS), classifying vaccination patterns as “recommended” (based on recommendations from the Advisory Committee on Immunization Practices [ACIP]), alternate (following ACIP recommendations with limiting of vaccinations per visit or skipping of at least 1 series)” or “unknown or unclassifiable” (not following ACIP recommendations or clearly limiting vaccinations or series).  

Of note: the researchers included hepatitis A and rotavirus vaccines in their up-to-date definition, which are relatively recent additions and not routinely reported by the CDC.

Overall, 63% of the children were classified as recommended, 23% as alternate, and 14% as unclassifiable or unknown. In total, 58% of the children were up to date with ACIP recommendations by age 19 to 35 months.

Compared with those following a recommended pattern, those following an alternate pattern were 4.2 times more likely to not be up to date. Those following unknown or unclassifiable patterns were ∼2.4 times as likely to not be up to date. No children who skipped vaccination series were considered up to date.

Of those children not up to date, approximately 66% had started at least 1 vaccination series late, and those considered up to date following an alternate pattern had ∼3 more vaccination-related visits and received 1 less vaccine per visit than up-to-date recommended-pattern children.

“The nonadherence of nearly 40% of the children in the 2014 NIS to the recommended schedule is consistent with several trends reported by American doctors in recent years, including parental requests to limit the number of vaccinations given at each visit, increased need for a strong and consistent physician recommendation for vaccination, and potentially wavering vaccine confidence.”

“Vaccine schedule adherence patterns are strongly associated with up-to-date status, and future research should be focused on identifying the parent actions and circumstances that increase the likelihood of deviating from the recommended schedule. Interventions should target both providers (to ensure that all eligible vaccines are offered) and parents (to ensure that all eligible vaccines are received), ultimately contributing to greater numbers of US children who are up-to-date for all recommended immunizations.”

—Michael Potts

Reference:
Hargreaves AL, Nowak G, Frew P, et al. Adherence to timely vaccinations in the United States [published online February 21, 2020]. Pediatrics. doi: https://doi.org/10.1542/peds.2019-0783.