Assessment of Average Days Undervaccinated for U.S. Children Using the National Immunization Survey Open Access

Kalmus, Grace (Spring 2020)

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Background: In the United States, childhood vaccination coverage is relatively high. However, increasing vaccine hesitancy and continued issues of access have led to increased delays in vaccination. While numerous metrics have been used to assess vaccination coverage, average days undervaccinated (ADU), a measure that accounts for every day of life a child is delayed, has not been assessed on a national level.

Methods: Weighted data from the 2017 National Immunization Survey – Child were used to assess vaccination delay among U.S. children ages 19 – 35 months. Vaccination delay was measured using the ADU metric, created by accounting for the time between when a child should have been vaccinated and when the child actually received the vaccination for every recommended dose. Linear and Poisson regression were used to assess the relationship between ADU, the number of vaccination providers a child saw, and other covariates of interest.

Results: In total, 68.2% of the children in the study population were undervaccinated for at least one day of life. Of these children with at least one day undervaccinated, the mean ADU was 94.3 days. ADU was higher for children with three or more vaccination providers than those with two, and was lowest for children with only one provider. Children who lived below the poverty level, were not the firstborn child, had a mother who was less than 30, and did not have private insurance were associated with an increased prevalence of having vaccine delay.

Conclusion: ADU is a measure of vaccine coverage that is more sensitive to vaccine delay than other measures commonly used. Factors associated with higher ADU can provide areas for public health intervention to decrease vaccine delay nationwide. 

Table of Contents

Literature Review 1

Vaccination Trends in the United States 1

Consequences of Not Vaccinating 2

Characteristics of Under- and Unvaccinated Children 5

Reasons for Vaccine Refusal and Alternate Schedules 6

Measures of Vaccination Status 7

Thesis Rationale 10

Introduction 12

Methods 13

Study Population 13

Study Variables 14

Average Days Undervaccinated 14

Predictor Variables 18

Data Analysis 18

Ethics 19

Results 20

Characteristics of Those With and Without Vaccine Delay 20

Mean ADU 20

Poisson Regression 21

Linear Regression 22

Discussion 23

Estimates of Vaccine Delay 23

Number of Providers and Vaccination Status 26

Additional Factors 28

Strengths and Limitations 31

Conclusion 32

Public Health Implications 33

References 35

Tables 43

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