Early Childhood Vaccination In Two Rural Counties -- Nebraska, 1991-1992

The national vaccination objectives for the year 2000 include increasing coverage for the recommended primary vaccination series * among children aged less than 2 years to at least 90% and to vaccinate at least 95% of school-aged children (1). Although baseline data for these two goals have been obtained in numerous urban settings (2), similar baseline data from rural populations are limited. To determine the vaccination status of children in rural Nebraska, where 51% (812,000) of Nebraska's residents live, the Nebraska Department of Health, in collaboration with Hastings College, conducted a retrospective study of school-aged children in grades kindergarten through six in two rural counties during the 1991-92 school year. This report summarizes the study findings.

These data reflect the vaccination status of children born in 1980-1986. Information abstracted from school records included county of residence, school, grade, date of birth, and dates of receipt of diphtheria and tetanus toxoids and pertussis vaccine (DTP), oral polio vaccine (OPV), and measles-mumps-rubella vaccine (MMR) required for school entry. All students exempted from vaccination under the state's statutory waiver clause and all students whose records lacked a date of birth were excluded from the analysis. The Nebraska school vaccination law (school law) requires three DTP, three OPV, and one MMR vaccination before a child enters school.

Age at vaccination was defined as the interval between date of birth and date of receipt for each of four doses of DTP, three doses of OPV, and one dose of MMR. Being up-to-date (UTD) was defined as having received three doses of DTP and two doses of OPV (3:2) by the first birthday, and as having received four doses of DTP, three doses of OPV, and one dose of MMR (4:3:1) by the second birthday.

Records for 3897 children were abstracted from all 23 schools in the two counties. Eighty-four (2%) records were excluded from analysis: 13 (0.3%) lacked dates of birth, 47 (1%) were for children who were exempt, and 24 (0.6%) had irreconcilable errors for dates of vaccination.

Of the remaining 3813 children, 3358 (88%), 3723 (98%), and 3766 (99%) received at least one dose of DTP or OPV by ages 3, 12, and 24 months, respectively. UTD rates at the first birthday (3:2), the second birthday (4:3:1), and on entry to school were 85%, 64%, and 99%, respectively (Table 1). The UTD rates for the complete series at 12 and 24 months were not significantly associated with the child's county of residence, school attended, grade, or year of birth.

Because of the declining UTD rates between 12 months and 24 months of age, vaccination patterns in the interval between 12 and 24 months of age were analyzed for all children UTD at age 12 months. Of the 3257 children UTD at age 12 months, 2365 (73%) were UTD at age 24 months. Of the remaining 892 children UTD at 12 months, 77% received one or two of the three required vaccinations and 23% received no vaccinations, therefore, failing to receive all vaccines needed to be UTD by age 24 months (Table 2).

A delay beyond 3 months of age in receiving the first dose of DTP or OPV was associated with not being UTD at both 12 (3:2 series) months and 24 (4:3:1 series) months of age. Among children who did not receive DTP or OPV by age 3 months, 242 (53%) of 455 were not UTD at age 12 months, compared with 314 (9%) of 3358 children who received DTP or OPV before age 3 months (relative risk (RR)=5.7). Similarly, for children who did not receive DTP or OPV by age 3 months, 297 (65%) of 455 were not UTD at age 24 months, compared with 1076 (32%) of 3358 for children who received DTP or OPV before age 3 months (RR=2.0).

Reported by: E Behrens, PhD, Hastings College, Hastings; J Libby, MA, G Borden, Div of Disease Control, T Safranek, MD, State Epidemiologist, Nebraska Dept of Health. Div of Immunization, National Center for Prevention Svcs; Div of Field Epidemiology, Epidemiology Program Office, CDC.

Editorial Note

Editorial Note: These findings indicate that 64% of rural Nebraska schoolchildren were UTD for vaccinations at their second birthday, a rate that is substantially higher than that recently observed in school children in urban areas in many cities in the United States (range: 10%-42%) (2). Nonetheless, additional efforts will be needed to increase national vaccination levels to 90% of children fully vaccinated by their second birthday.

In rural Nebraska, as well as in previous studies in 11 U.S. cities (2,3), delay in obtaining the first dose of either OPV or DTP was an important predictor of failure to be UTD at 12 and 24 months of age. If 90% of the children receiving their first vaccination after 3 months of age and before 12 months of age had been brought UTD through aggressive follow-up by the vaccination provider, the 3:2 UTD rate at 12 months would have increased from 85% to 94%.

The current recommendation for simultaneous administration of vaccines was not made until 1986 (4). Had this recommendation been in effect, 77% of children UTD at 12 months but not at 24 months of age could have been UTD at 24 months. Ensuring simultaneous administration of needed vaccines to at least 90% of the children who, although UTD at age 12 months were not UTD at age 24 months, would increase the coverage levels for being UTD with the 4:3:1 series among this subset of children from 73% to 92%. However, even with improved tracking, follow-up, and the elimination of missed opportunities, coverage for the overall 4:3:1 series would have reached only 87%. Therefore, in rural Nebraska, additional strategies are needed to reach the national year 2000 objective.

Reasons for failure of children to appear on time for their first vaccination have not been well characterized. Regardless of when a child receives the first vaccination, the first visit generates a vaccination-provider record. To reduce the number of children who do not receive any vaccinations before age 3 months in rural Nebraska, a pilot follow-up system is planned in which the mother, after delivery and before hospital discharge, will complete a postcard with the name of the infant's intended vaccination provider. The hospital will then send the postcard to the indicated provider, who in turn will contact the infant's caregiver if the infant has not visited the provider by age 3 months.

Based on the results of this study, vaccine providers in rural Nebraska can make substantial gains in vaccination coverage by 1) focusing additional efforts toward children who receive their first vaccination after age 3 months and 2) simultaneously administering vaccines due between age 12 and 24 months.

References

1. Public Health Service. Healthy people 2000: national health

promotion and disease prevention objectives. Washington, DC: US Department of Health and Human Services, Public Health Service, 1991; DHHS publication no. (PHS)91-50213. 2. CDC. Retrospective assessment of vaccination coverage among school-aged children -- selected U.S. cities, 1991. MMWR 1992;41:103-7. 3. CDC. Early childhood vaccination levels among urban children -- Connecticut, 1990 and 1991. MMWR 1992;40:888-91. 4. CDC. New recommended schedule for active immunization of normal infants and children. MMWR 1986;35:577-9.

• Recommended series includes four doses of diphtheria and tetanus toxoids and pertussis vaccine (DTP); three doses of oral polio vaccine (OPV); one dose of measles-mumps-rubella vaccine (MMR); three or four doses of Haemophilus influenzae type b conjugate vaccine, depending on type of vaccine used; and three doses of hepatitis B vaccine.

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