Retrospective Assessment of Vaccination Coverage Among School-Aged Children -- Selected U.S. Cities, 1991

Preschool-aged children are at increased risk for vaccine-preventable diseases; outbreaks of these diseases in this age group occur predominately among unvaccinated children (1). In the United States, vaccination rates of individual antigens required for children at the time they enter school are greater than 95%; however, vaccination rates for children at their second birthday are substantially lower (2) despite recommendations by the Immunization Practices Advisory Committee (ACIP) and the American Academy of Pediatrics that all children complete a schedule of vaccination by age 15-18 months.* To retrospectively assess vaccination levels among school-aged children at their second birthday, CDC, in collaboration with state and local health departments, is conducting surveys of vaccination levels among children entering school who reside in the 60 largest U.S. cities. This report presents findings from surveys completed in nine cities ** during 1991.

These surveys use a multistage cluster survey design in which public and private schools are randomly selected in proportion to their estimated size (5). At each school, health records for kindergarten or first-grade students aged 4-7 years are randomly selected and the dates of vaccinations abstracted. Vaccination status is assessed for each child at age 3 months (92 days) and at the second birthday (732 days). Vaccination levels for two different combinations of vaccine doses are determined: four doses of diphtheria and tetanus toxoids and pertussis vaccine (DTP), three doses of oral poliomyelitis vaccine (OPV), and one dose of measles, mumps, and rubella vaccine (MMR) (4:3:1) or three doses of DTP, three doses of OPV, and one dose of MMR (3:3:1). In addition, individual coverage levels are determined for the third and fourth doses of DTP (DTP3, DTP4), third dose of OPV (OPV3) and one dose of MMR. *** Coverage rates are calculated both for all vaccines administered at any age and for only vaccines administered at the recommended ages and intervals (i.e., strict definition for timing of valid doses). ****

For the nine cities surveyed, the proportion of children who were up-to-date with valid doses by their second birthday, based on the 4:3:1 schedule, ranged from 10% in Houston to 42% in El Paso (Table 1); however, with a 3:3:1 schedule, vaccination rates were higher (range: 40% (Houston) to 61% (El Paso)). In addition, when up-to-date vaccination levels for the 4:3:1 schedule were determined without application of the strict definitions for timing of valid doses, the coverage rates increased by 1%-6% for the nine cities.

When evaluated individually, vaccination levels for specific antigens were higher than vaccination levels for the complete vaccination series (Table 1). Vaccination coverage rates by the second birthday were 11%-47% for DTP4, 53%-77% for OPV3, and 52%-71% for MMR. In the nine cities, 61%-72% of children did not receive DTP4 at the time they received MMR.

On average, 90% of children had received at least one vaccination before their first birthday (range: 79% in Miami to 96% in Cleveland). Of all children surveyed, 83%-98% had had at least one contact with vaccination services by age 2 years. Most children began the vaccination series on time: 53%-73% were vaccinated by age 3 months. Children whose vaccination series was up-to-date by age 3 months (i.e., had received the first dose of DTP and OPV) were 3.1 times more likely (range: 2.7-17.0 times) to be up-to-date with the 4:3:1 combination by their second birthday than those not up-to-date by age 3 months (Table 2). However, fewer than half completed their primary series at age 2 years, even among those who were up-to-date at age 3 months (Table 2).

Reported by: D Alford, Cleveland Dept of Public Health; J Kelly, TJ Halpin, MD, State Epidemiologist, Ohio Dept of Health. L Nickey, MD, El Paso City-County Health District; R Crider, J Arrandondo, MD, Houston Dept of Health; DM Simpson, MD, State Epidemiologist, Texas Dept of Health. A Kimbler, Dade County Public Health Unit; H Janowski, Florida Dept of Health and Rehabilitative Svcs. J Labat, MD, New Orleans School Board; B Lutz, MD, City of New Orleans Public Health Dept; J Nitzkin, MD, Louisiana Dept of Health and Hospitals. S Friedman, MD, New York City Dept of Health. GW Rutherford Jr, MD, State Epidemiologist, California Dept of Health Svcs. D Sharma, PhD, Health Commissioner, City of St. Louis; L Speissegger, M Sanderson, C Butler, M Klatt, J Strong, HD Donnell Jr, MD, State Epidemiologist, Missouri Dept of Health. ME Levy, MD, District Epidemiologist, District of Columbia Commission of Public Health. Div of Immunization, National Center for Prevention Svcs, CDC.

Editorial Note

Editorial Note: One of the national health objectives for the year 2000 is to vaccinate 90% of children with the primary series by their second birthday (objective 20.11) (1). However, during the mid- to late 1980s, vaccination levels in the nine major U.S. cities reported here were substantially below the stated 90% goal and lower than levels in other reports (2,6). For example, during 1985, national estimates of vaccination levels for individual antigens ranged from 77% to 86% for children age 2 years (CDC, unpublished data, 1985) compared with levels that ranged from 52% to 84% in this report. However, the 1985 findings were based on a national sample and did not represent the large urban areas that constituted the populations sampled for these retrospective surveys.

Low vaccination rates with the recommended 4:3:1 schedule have been attributed, in part, to the difficulty of administering the DTP4 dose on schedule. However, even without DTP4, the rates are substantially less than the year 2000 objective. Although OPV3 and DTP4 are both recommended for children at age 15 months, OPV3 coverage substantially exceeded DTP4 coverage primarily because 35%-78% of children receiving OPV3 did so during the first rather than the second year of life. Furthermore, findings indicated that many children failed to receive DTP4 at their MMR visit. In 1986, ACIP recommended that DTP4 and MMR be administered at the same visit; had these recommendations been in effect and adhered to when these children were aged 15-18 months, coverage of DTP4 and the 4:3:1 series could have been higher (7). Each contact with health-care providers represents an opportunity to educate parents about the recommended vaccination schedule and the importance of completing the schedule on time.

The findings in this report confirm previous findings regarding children who had not received the first doses of DTP and OPV by age 3 months and who, therefore, were at increased risk for not being up-to-date by their second birthday (8,9). Parents of children who begin the vaccination series late should be targeted for intensive education, and greater efforts are needed to track these children to assure they return for follow-up doses.

To improve vaccination levels by age 2 years among children in the United States, CDC has begun the Infant Immunization Initiative. As part of this initiative, each state and local health department is encouraged to measure current vaccination levels and develop strategies to improve them. The retrospective survey method described in this report is easy to implement, can be completed rapidly and inexpensively, allows different outcome measurements of vaccination levels at different ages, and provides reliable data based on school records that are easy to review. Even though these retrospective surveys cannot detect recent changes in vaccination levels, when regularly conducted statewide they can be used to monitor secular trends in vaccination levels.

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. Measles vaccination levels among selected groups of preschool-aged children--United States. MMWR 1991;40:36-9.

3. CDC. General recommendations on immunization. MMWR 1989;38:205-14,219-27.

4. ACIP. Hepatitis B virus: a comprehensive strategy for eliminating transmission in the United States through universal childhood vaccination--recommendations of the Immunization Practices Advisory Committee (ACIP). MMWR 1991;40(no. RR-13).

5. CDC. Sampling procedure for conducting immunization assessment/validation surveys for school and day-care centers--retrospective surveys using school systems databases and guidelines for public health immunization clinic audits for immunization project areas. Atlanta: US Department of Health and Human Services, Public Health Service, CDC, National Center for Prevention Services, 1990.

6. Bernier RH. Assessment for program management. Proceedings of the 21st immunization conference. Washington, DC: June 10-14, 1991.

7. CDC. New recommended schedule for active immunization of normal infants and children. MMWR 1986;35:577-9.

8. Eddins DL, Sirotkin BI, Holmgreen P, Russell S. Assessment and validation of immunization status in the United States. Proceedings of the 20th immunization conference. Dallas: May 6-9, 1985:51-61.

9. CDC. Early childhood vaccination levels among urban children-- Connecticut, 1990 and 1991. MMWR 1992;40:888-91.

• The ACIP recommends vaccination that includes four doses of

diphtheria and tetanus toxoids and pertussis vaccine; three doses of oral poliomyelitis vaccine; one dose of measles, mumps, and rubella vaccine; and a complete series for Haemophilus influenzae type b --either three or four doses, depending on the type of vaccine. In late 1991, hepatitis B vaccine was recommended for universal vaccination of infants (3,4).

** Cleveland; El Paso and Houston, Texas; Miami; New Orleans; New York City (Bronx); Oakland, California; St. Louis; and Washington, D.C.

*** Haemophilus influenzae type b vaccination status was not evaluated because this vaccine is not required for school entry in all states and data are not available in school records.

**** Strict definition for timing of valid doses are as follows: the first DTP dose must be given after 42 days (6 weeks) of age with dose two and three each given after a minimal interval of 28 days. The fourth DTP dose must be given at least 180 days after dose three. For OPV, the first dose must be given after 42 days (6 weeks) of age, with dose two given a minimum of 42 days after the first dose. The third dose of OPV must be given a minimum of 42 days after the second dose. Any dose of MMR given on or after the first birthday was defined as a valid dose. Children with health records that were not located ( less than 4% of all children assessed in all schools) were defined as not vaccinated. Only records that had dates for all vaccinations administered were assessed as valid.

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