Number of Childhood and Adolescent Vaccinations Administered Before and After the COVID-19 Outbreak in Colorado

Abstract

This study assesses the association of social distancing due to coronavirus disease 2019 (COVID-19) with immunizations administered by age category (0-2 years, 3-9 years, and 10-17 years) in Colorado.

As a consequence of the social distancing measures that have been implemented in many parts of the United States, medical visits to primary care physicians have dropped as some parents and patients worry that they could be put at risk for contracting coronavirus disease 2019 (COVID-19).¹ The American Academy of Pediatrics has issued guidance suggesting that preventive visits, including vaccination, should continue, particularly for younger children.² In this report, we assessed the number of childhood and adolescent vaccinations administered in the months before and after the start of the COVID-19 outbreak in Colorado.

Methods

Data were pulled from the Colorado Immunization Information System. Approximately 87.5% of known immunizing health care professionals report to the Colorado Immunization Information System. All children younger than 6 years have an immunization record in the system, and 85.2% of vaccinations administered in 2019 to individuals aged 0 to 18 years were reported to the Colorado Immunization Information System within the same day. The Colorado Department of Public Health and Environment ethics review deemed this as exempt research with no need for informed consent.

Using data from January 5, 2020, to May 2, 2020, an interrupted time series analysis was used to measure the association of COVID-19 with immunizations administered. Three age categories were reported (0-2 years, 3-9 years, and 10-17 years) to reflect the recommended US childhood vaccination schedule. Combination vaccines counted as a single dose. Total number of vaccinations administered were reported as were 3 specific vaccines (Haemophilus influenzae type b; 13-valent pneumococcal conjugate; and measles, mumps, and rubella vaccines) because of the potential for spread to infants within a household and the potential for outbreaks.

Social distancing measures were implemented in Colorado on March 15, 2020. A linear mixed model with autoregressive correlation matrix was used with social distancing period, time in weeks, and the interaction of social distancing period and time as the primary explanatory variables. The trend before week 12 was assumed to be consistent across the age categories. However, the level change and trend after week 12 was allowed to differ between age categories with the use of interaction terms. Autocorrelation was assessed with the Durbin-Watson statistic. Data were analyzed using SAS statistical software version 9.4 (SAS Institute). All statistical tests were performed as 2-sided tests with a level of significance of .05.

Results

From January 5 through March 15, 2020 (weeks 1-11), the mean (SD) number of vaccinations administered per week was 23 523 (2181), 6148 (1049), and 8318 (933) for individuals aged 0 to 2 years, 3 to 9 years, and 10 to 17 years, respectively. After March 15 (weeks 12-18), the mean (SD) number of doses administered for the same age groups was 16 146 (1648), 1330 (408), and 1529 (623), respectively. This equates to a drop in mean immunization rate between time periods of 31% for individuals aged 0 to 2 years, 78% for those aged 3 to 9 years, and 82% for those aged 10 to 17 years.

All age groups had a significant drop in immunizations immediately following social distance guidance release (March 15, 2020). In individuals aged 0 to 2 years, the rate of immunizations dropped by 4581 (95% CI, 2965-6196) immunizations per week (P < .001). In individuals aged 3 to 9 years, it dropped by 2486 (95% CI, 568-4408) immunizations per week (P > .99), and in individuals aged 10 to 17 years, it dropped by 4060 (95% CI, 2156-5965) immunizations per week (P < .001) (Figure 1). While the pre–social distancing trend was declining by 405 (95% CI, 203-607) immunizations per week, the post–social distancing trends were not significant for all age categories. Trends were similar for Haemophilus influenzae type b; 13-valent pneumococcal conjugate; and measles, mumps and rubella vaccines (Figure 2).

Figure 1. Interrupted Time Series Analysis for Total Vaccine Doses Administered, January 5 Through May 2, 2020, by Age Group.

For birth to 15 months, reflected in this report as 0- to 2-year-olds, the immunization schedule recommends 4 doses of diphtheria, pertussis, and tetanus vaccine; 3 doses of inactivated polio vaccine; 2 to 3 doses of rotavirus vaccine; 3 doses of hepatitis B vaccine; 3 to 4 doses of Haemophilus influenzae type b vaccine; 4 doses of 13-valent pneumococcal conjugate vaccine; 1 dose of measles, mumps, rubella vaccine; 1 dose of varicella vaccine; 2 doses of hepatitis A vaccine; and 1 to 2 doses of annual influenza vaccine. Children aged 3 to 9 years are recommended to receive 1 dose of diphtheria, pertussis, and tetanus vaccine; 1 dose of inactivated polio vaccine; 1 dose of measles, mumps, rubella vaccine; 1 dose of varicella vaccine (at 4-6 years of age); and 1 to 2 doses of annual influenza vaccine. Children and adolescents aged 10 to 17 years are recommended to receive 1 dose of tetanus, diphtheria, and pertussis vaccine; 2 doses of quadrivalent meningococcal conjugate vaccine; 2 to 3 doses of human papillomavirus vaccine; and 1 dose of annual influenza vaccine.

Figure 2. Interrupted Time Series Analysis for Specific Vaccine Doses Administered, January 5 Through May 2, 2020, for Individuals Aged 0 to 2 Years.

Discussion

Since the onset of the COVID-19 pandemic, vaccination uptake in children and adolescents has shown a significant decrease in Colorado. While the clinical implications of our observation are not yet known, public health advocates should consider addressing this drop to avoid the potential for vaccine-preventable diseases. Primary care professionals should consider implementing reminders and recalls to parents,³ and local and state health departments should consider implementing immunization registry-based recall.⁴ Limitations of this report include its ecological nature, being limited to a single state, and the potential for missing data.