Estimating risk factors for delays in childhood immunization using the National Health Interview Survey.

Abstract

This study demonstrates the importance of the distinction between up-to-date and age-appropriate vaccination status in risk factor analysis and performance measurement. A retrospective cohort analysis using a sample of 9,223 children 25--72 months of age from the 1992--1996 National Health Interview Survey (NHIS) was conducted to determine if the DTP4, third polio, and MMR1 vaccine doses were received age-appropriately and if not, length of delay was calculated. Risk factors were estimated using logistic regression models, and policy simulations were conducted to assess the potential benefits of removing existing barriers to age-appropriate vaccination. Only 46% of children received the DTP4 dose age-appropriately, while 64% received the third polio dose, and 57% the MMR1 dose age-appropriately. Black race, urban residence, absence of a two-parent household, large family size, high school education level or less, no insurance coverage, and no household telephone were significantly related to an increased likelihood of delay for each the DTP4, polio3, and MMR1 doses (p ≤ .05). Male gender, non-Hispanic ethnicity, suburban residence, poverty level, Medicaid enrollment, and absence of a usual provider were also significantly related to increased likelihood of vaccination delay for one or more of these vaccine doses (p ≤ .05). Of these risk factors, suburban residence, two-parent household, poverty status, education level, insurance coverage, Medicaid eligibility, and no household telephone were found to be statistically significant only in risk models of vaccination delay and not in risk models of up-to-date vaccination status. The results of this study illustrate that removal of key access barriers, such as not having health insurance or a usual source of medical care, can substantially reduce vaccination delay. Despite the removal of these barriers, some children still have exceedingly high likelihood of vaccination delay, suggesting that interventions that focus on these high-risk populations may be necessary to minimize vaccination delay. While surveillance of vaccination coverage rates remains an important public health function, the results of this study suggest that age-appropriate vaccination status should also be monitored.