Introduction
Monitoring the trends in undervaccination, including that because of parental vaccine
refusal or delay, can inform public health responses directed at improving vaccine
confidence and vaccination coverage.
Methods
A retrospective cohort study was conducted in the Vaccine Safety Datalink. The cohort
included all children born in 2004–2017 with ≥3 well-child visits between ages 2 and
23 months. Using electronic health record–based vaccination data, the average days
undervaccinated was calculated for each child. Undervaccination patterns were assessed
through age 23 months. Temporal trends were inspected for inflection points and were
analyzed using linear regression. Nested within the cohort study, a survey was conducted
to compare parent reports of vaccine refusal or delay with observed vaccination patterns.
Data were analyzed in 2020.
Results
The study cohort consisted of 808,170 children. The percentage of children with average
days undervaccinated=0 (fully vaccinated, no delays) rose from a nadir of 47.1% for
the birth year 2008 to 68.4% for the birth year 2017 (ptrend<0.001). The percentage with no vaccines rose from 0.35% for the birth year 2004 to
1.28% for the birth year 2017 (ptrend<0.001). Consistent vaccine limiting was observed in 2.04% for the birth year 2017.
Omission of measles, mumps, and rubella vaccine peaked at 4.76% in the birth year
2007 and declined thereafter (ptrend<0.001). On the parent survey (response rate 60.2%), a high proportion of parents
of the most undervaccinated children reported refusing or delaying vaccines.
Conclusions
In a 14-year cohort study, vaccination timeliness has improved. However, the small
but increasing number of children who received no vaccines by age 23 months warrants
additional attention.
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Article Info
Publication History
Published online: April 29, 2021
Identification
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© 2021 American Journal of Preventive Medicine. Published by Elsevier Inc. All rights reserved.
