Early Childhood Vaccination Levels Among Urban Children -- Connecticut, 1990 and 1991

In the United States, the high incidence of measles among urban preschool-aged children who had not received age-appropriate vaccination has focused attention on the adequacy of and barriers to early childhood vaccinations (1-3). To assess early childhood vaccination levels of urban Connecticut children, during fall 1990 and spring 1991, the Connecticut Department of Health Services conducted retrospective surveys of first-grade students in Hartford and New Haven, both with populations greater than 100,000 persons.

A random classroom-cluster survey technique (CDC, unpublished data) was used to select a sample of 666 Hartford and 810 New Haven first-grade students to review their school vaccination records. Primary outcome measures were 1) timeliness of receipt of a first dose of diphtheria and tetanus toxoids and pertussis vaccine (DTP) (by 3, 6, and 12 months of age) and 2) completion, by the second birthday, of the primary vaccination series * required by state statute for school entry. Possible predictors of outcomes abstracted from each record included the student's race/ethnicity and socioeconomic status (SES). SES was determined by per capita income of census tract of residence (both cities) or free-lunch status (New Haven). In addition, student name and birthdate were linked with state birth-certificate information on maternal residence at birth to determine which students were in-migrants (having moved into the respective survey areas after birth).

The study populations were predominantly poor (e.g., in New Haven greater than 60% qualified for free-lunch program) and minority (Hartford: 37% black and 55% Hispanic; New Haven: 59% black and 19% Hispanic). Nearly one third were in-migrants (Hartford 34%, New Haven 28%).

Completion rates for a first dose of DTP by age 3 months (90 days) ranged from 67% in Hartford to 77% in New Haven. By age 6 and 12 months, respectively, more than 89% and 93% of children in each city had received a first dose of DTP. Completion rates for the seven required antigens by the second birthday were 67.2% (95% confidence interval (CI)=64.5%-69.9%) for Hartford and 70.8% (95% CI=68.4%-73.2%) for New Haven. Completion rates for measles vaccination by the second birthday were 78.1% (Hartford) and 79.0% (New Haven).

Of the demographic information, only place of residence at birth was a predictor of incomplete vaccination. In-migrant children were significantly more likely in both cities to be incompletely vaccinated by their second birthday than were children born in the survey area (Hartford: 24% versus 44%; New Haven: 25% versus 39%; p less than 0.001 for both).

Vaccination status at age 3 months was the strongest predictor of failure to complete vaccination with each antigen and the entire series by the second birthday (Table 1). When analyzed by the in-migrant status, failure to be vaccinated by age 3 months remained a strong predictor of failure for later completion for each antigen and the entire series. In addition, for children in both cities, the time interval between receiving a first and a second DTP dose was longer for children who received a first DTP dose after age 3 months than for children who received a first dose before age 3 months (median intervals: 80 days and 63 days, respectively, for Hartford; 84 days and 63 days, respectively, for New Haven).

On the basis of these findings, the Connecticut Department of Health Services has initiated studies in both cities to determine maternal, infant, social, and vaccine-delivery factors associated with failure to receive a first dose of DTP as recommended. Reported by: E Chiao, E Drew, J Petrini, W White, DVM, Dept of Epidemiology and Public Health, Yale Univ, New Haven; K Hayes, MSN, Dept of Community Medicine, Univ of Connecticut, Farmington; D Bullard, J Hadler, MD, State Epidemiologist, Connecticut Dept of Health Svcs. Div of Immunization, National Center for Prevention Svcs, CDC.

Editorial Note

Editorial Note The importance of age-appropriate vaccination in the United States is underscored by one of the national health objectives for the year 2000--that at least 90% of children should be completely vaccinated by 2 years of age (4). Although the measure of complete vaccination among 2-year-olds in the surveys in Connecticut required three doses of DTP instead of four, as recommended by the Immunization Practices Advisory Committee (ACIP) and the American Academy of Pediatrics (AAP), levels in both cities were substantially less than this objective. In general, when four doses of DTP are used as the measure, age-appropriate levels of vaccination are 15%-20% lower (5).

A particularly important finding in Connecticut was that 23%-33% of children had not received a first dose of DTP by age 3 months; both the ACIP and the AAP recommend the dose be given by age 2 months (6,7). This finding suggests, in part, that many children were not effectively referred from perinatal care to a first vaccination appointment. Accordingly, barriers to receipt of an age-appropriate first vaccine dose must be identified.

The findings in Connecticut are consistent with those from other studies (5) that have indicated that untimely initial vaccination is a marker for delay in receipt of a second dose of DTP vaccine, as well as for failure to complete each required vaccine and the entire primary vaccination series by 2 years of age. Early (i.e., at birth or when the first dose is missed) identification of children at risk for missing their first dose of DTP would enable them to be targeted for intensive follow-up to minimize the delay in receiving appropriate vaccinations.

Beginning vaccination in the first few months of life is particularly important for the prevention and control of Haemophilus influenzae type b and pertussis. The risk for severe morbidity is highest for both diseases in the first year of life. However, vaccine efficacy against each is optimal only following multiple doses of vaccine. The findings in this report indicate that, in Connecticut, as many as one third of urban children may be at prolonged and unnecessary risk for these diseases. Although the Connecticut data show that 93% of children have received a first DTP dose by age 1 year, program attention needs to focus on tracking from birth and prompt follow-up, including outreach for infants who are behind schedule to assure that at least 90% of children begin vaccination by age 3 months.

In Connecticut, many students born outside the sampled areas had markedly lower age-appropriate vaccination rates. This finding suggests that some parents are not enrolling their children in the preventive health-care system of the area to which they have moved. Accordingly, strategies are necessary to identify and provide vaccination to these children soon after their arrival.

To improve vaccination levels by age 2 years among preschool-aged children in the United States, CDC has begun an Infant Immunization Initiative. As part of this initiative, each state and local health department is encouraged to measure initial vaccination levels of children in urban areas and develop strategies to improve them. In addition, in areas with substantial in-migration of preschool-aged children, the vaccination status of children should be evaluated and, if indicated, special strategies developed to ensure timely vaccination of the children. Enforcement of requirements for age-appropriate vaccination for children attending licensed day-care centers is one measure that may improve vaccination levels.

References

1. CDC. Measles--United States, 1989 and first 20 weeks 1990. MMWR 1990;39:353-5,361-3.

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

3. National Vaccine Advisory Committee. The measles epidemic: the problems, barriers and recommendations. JAMA 1991;266:1547-52.

4. 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) 91-50213:76,122.

5. Eddins DL, Sirotkin BI, Holmgreen P, Russell S. Assessment and validation of immunization status in the United States. 20th Immunization Conference: Proceedings. Dallas: May 6-9, 1985:51-5.

6. ACIP. Diphtheria, tetanus and pertussis: recommendations for vaccine use and other preventive measures--recommendation of the Immunization Practices Advisory Committee (ACIP). MMWR 1991;40(no. RR-10).

7. American Academy of Pediatrics Committee on Infectious Diseases. Pertussis. In: Report of the Committee on Infectious Diseases, 22nd edition. Elk Grove Village, Illinois: American Academy of Pediatrics, 1991:358-69.

• Three doses of DTP; three doses of oral or inactivated polio vaccine; and one dose each of vaccine against measles, mumps, and rubella.

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