Pediatric Routine Immunization Delays in Chicago Before and After the Onset of the COVID-19 Pandemic: A Time-to-Event Analysis

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Abstract
Objectives: Decreases in routine vaccination have been reported since the COVID-19 pandemic. To identify age groups and vaccine types potentially affected by pandemic disruptions and vaccine hesitancy, we assessed routine vaccination delays among children in Chicago before and after the onset of the COVID-19 pandemic. Methods: We used the Illinois Comprehensive Automated Immunization Registry Exchange to estimate the median time to vaccination after eligibility, vaccination incidence rates, and hazard ratios for vaccination of children and adolescents aged ≤18 years vaccinated in 2018-2019 (pre–COVID-19) and 2021-2022 (post–COVID-19 onset). We established 3 age categories: early childhood (0-3 y), childhood (4-6 y), and adolescence (11-18 y). Results: The post–COVID-19 onset cohort had a greater number of median (IQR) days to vaccination than the pre–COVID-19 cohort for adolescent vaccines (249 [86-624] vs 219 [69-614] d). The post–COVID-19 onset cohort had greater median days of delays by dose than the pre–COVID-19 cohort did, specifically for human papillomavirus (HPV) dose 2 (difference of 91 d); HPV dose 3 (52 d); inactivated poliovirus dose 4 (51 d); and diphtheria, tetanus, and acellular pertussis dose 5 and tetanus, diphtheria, and acellular pertussis dose 1 (43 d). In adjusted models, hazards (instantaneous rate of vaccination) were lower for the post–COVID-19 onset cohort than for the pre–COVID-19 cohort, particularly for vaccinations recommended for children aged 4 to 6 years and adolescents, indicating greater postpandemic onset delays for these groups. Conclusions: Vaccination delays after the COVID-19 pandemic were greatest among children aged 4 to 6 years and adolescents. Clinicians should verify the vaccination status of these groups to prioritize catch-up vaccinations, especially vaccines not required for school or childcare.

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