Background. Pediatric immunization rates have increased in the United States since 1990. Nevertheless, national survey data indicate that up to one third of 2-year-old children in some states and urban areas lack at least one recommended dose of diphtheria–tetanus–pertussis (DTP)-, polio-, or measles-containing vaccines. Immunization has become a key measure of preventive pediatric health care in the United States. To achieve and maintain the national immunization goal that 90% of children receive all recommended immunizations by 2 years of age, the role of the health care system in immunization delivery must be examined. Urban eastern Virginia has a diverse population that obtains immunization services from public, private, and military providers and insurers. At the time of this survey, immunization services in Virginia were available free to all children through public health clinics and to military families when using a military facility.

Objective. To examine access to pediatric immunization services and health system factors associated with underimmunization in a representative sample of children at 12 and 24 months of age.

Methods. We conducted a household survey in urban eastern Virginia from April through September 1993. A total of 12 770 households in Norfolk and Newport News, VA, were selected for inclusion in the study using probability-proportionate-to-size cluster sampling. Use of probability-proportionate-to-size sampling ensured that children within each city had equal probability of being included in the survey. Selected households were visited by trained interviewers to determine their eligibility, defined as having at least one child 12 to 30 months of age residing in the household. In eligible households, parents were asked to participate in a standardized, 15-minute interview. Survey respondents were asked about household demographics, and for each eligible child, the immunization history, health insurance, the name and location of all immunization providers, the usual immunization provider, and any problems the parent had experienced accessing immunization services with that child. Up-to-date (UTD) immunization status was defined as having all recommended doses of DTP, polio, and measles–mumps–rubella at 12 months (three DTP and two polio immunizations) and 24 months (four DTP, three polio, and one measles–mumps–rubella immunizations). The child's immunization history was assessed from parent and provider records only. Data analysis accounted for the survey's cluster sampling design (ie, within-cluster correlation). Because the immunization rates of the two cities did not differ significantly, unweighted analyses were used for ease of computation. Significance was determined for contingency tables by Wald's χ2 test.

Results. A total of 749 children (91% of eligible households) participated in the survey. Study children were born between October, 1990, and July, 1992. Immunization records were obtained for 705 children (94%). Eighty-seven percent of respondents were mothers, 44% were African-American, 40% of children were military dependents, and 40% were enrolled in the Women, Infants and Children (WIC) program. Sixty-five percent of children were UTD at 12 months and 53% at 24 months. Parents reported that their children's usual immunization providers were private doctors (34%); public health, hospital clinics, or community health centers (32%); and military clinics or a military contract provider (34%). At least one problem accessing immunization services was reported by 35% of respondents, ranging from 29% among those who used a private doctor as their child's usual immunization provider to 46% among those using a military contract provider. Overall, the most commonly reported problem was clinic waiting time (12%), with reports of waiting time as a problem occurring most often among those using the military contract provider (22%) and public health clinics (17%). The second most common problem was difficulty obtaining a timely appointment (10%), with appointment problems ranging from 18% to 24% among those using military facilities compared with 4% to 6% among those using other providers. Some of the other problems reported were taking time away from work, office hours, cost, and transportation, with the frequency varying by type of usual provider.

Household risk factors for children not being UTD at 12 and 24 months included having a greater number of children, single parenthood, lack of education beyond high school, teenage mother, African-American ethnicity, and not finding the child's immunization record at home. After adjusting for these household factors by multiple logistic regression, the system-related factors significantly associated with not being UTD at 12 months were not being in WIC (odds ratio [OR] = 2.1, 95% confidence interval [CI] 1.4–3.3), having Civilian Health and Medical Program of the Uniformed Services (OR = 5.2; CI: 2.9–9.5) or Medicaid (OR = 2.7; CI: 1.4–5.3) insurance, longer clinic waiting time (for each hour, OR = 1.6; CI: 1.2–2.0), and transportation problems (OR = 2.6; CI: 1.3–5.2); and at 24 months were not being in WIC (OR = 2.0; CI: 1.1–3.7), problems obtaining an appointment (OR = 4.5; CI: 1.8–8.6), and use of a military contract clinic (OR = 5.6; CI: 2.6–11.9). Although not all reported problems accessing services were independent risk factors for underimmunization, a dose–response relationship was found between the total number of different reported problems and children not being UTD at 24 months.

Conclusions. This is the first population-based study of the association between immunization coverage rates and access to public, private, and military health care systems. Overall, one third of parents perceived barriers to pediatric immunization services, and parent-reported problems accessing services had a dose–response association with underimmunization. The most commonly reported problems were long waiting times and difficulty obtaining appointments, but the pattern and magnitude of problems reported differed among public, private, and military services. Despite free immunizations, parents most often reported problems accessing public and military providers. Thus, parents did not necessarily consider cost-free and geographically available pediatric services to be barrier-free. Enrollment in WIC was associated with significantly increased immunization rates, although this study was conducted before linkage of the WIC program with immunization services. This finding suggests the importance of WIC as a point of access to the health care system for vulnerable families. In this population, significant variation in immunization rates was found among health care providers and insurers that was not readily explained by measured population characteristics or parent-reported access barriers, possibly attributable, in part, to differences in provider practices. Population-level measurement of immunization rates and parent perception of services is critical for improving access to, and quality of, immunization services.

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