Maryland conducts population-based assessments to determine immunization coverage, and compliance with school immunization regulations. Immunization coverage has been assessed by two types of studies: two-year-old surveys and retrospective kindergarten surveys. Data were obtained from 1977 to 1981 through surveys using a random sample of birth certificates to select two-year-old children. Low response rates (from 61% to 80%) were one of the limitations of this approach.

Since 1988/89, immunization coverage data for younger children has been obtained retrospectively through annual surveys of the immunization records of school enterers. The most recent estimates of immunization coverage of young children in Maryland are based on the 1998/99 retrospective survey of kindergarten enterers (See above map).

Kindergarten attendance in Maryland is mandated by law and is nearly universal. A total of 120 public and private schools were selected with chance of selection proportional to Kindergarten enrollment. In each selected school, the dates of immunization were abstracted from school records for each of 25 randomly selected children (or for all children if 25 or fewer were enrolled), yielding a total sample size of 2,741. The reported immunization coverage levels are the estimated coverage of kindergartners, when they were 24 months old.

In general, immunization status at 24 months of age has improved gradually since the 1988/89 survey. For polio, rates dropped for children in birth cohorts from 1982/83 to 1989/90. A change in the immunization schedule may have been in part responsible for this decline. In the early 1980’s the third dose of polio was delayed from 6 months to 15 months of age. After the mid 1980’s, the schedule was changed back to allow a third dose at 6 months, and immunization levels rose.

For other diseases, there were also little gains in coverage levels in children born from 1983/84 to 1985/86. This may in part be explained by the decreased commitment to resources and funding for immunization programs, which followed a period in the U. S. when enormous gains were made in the control of vaccine-preventable disease.

New vaccines and immunization initiatives in the 1960’s and 1970’s had given the impression that the battle against vaccine-preventable disease had been won. Resources and funding for immunization programs increased after the 1989/91 measles resurgence, and immunization levels have gradually risen.

The second method of estimating immunization levels is the National Immunization Survey (NIS). The completion rates for the State were numerically higher than last year’s rate, 79% (see table 1). However, at 77.1%, the completion rate for Baltimore City dropped below the national average.

This year’s rate for the State is down from the high reached on the 1997 NIS, in which Maryland posted a completion rate of 82% vs. the national average that year of 78%. This year’s rate for Baltimore City is also down from the high reached in 1996-1997 of 85%. Figure 1 shows Maryland and Baltimore City’s immunization completion rates since 1994.

The Center for Immunization remains committed to eventually reaching the goal of 90% completion of immunizations, 4:3:1, by two years of age.

Table 2 depicts the results of the 1999-2000 School Immunization Validation Review. Center for Immunization staff review immunization records in 100 or more schools each year over the past several years. Results have shown that compliance with Maryland's Immunization Regulations is about 10% lower in private schools than in public schools. The greatest area of low compliance is the 2nd MMR for kindergarten enrollees.

Table 1. Estimated Vaccination Coverage in Percent with Individual Vaccines and Vaccination Series Among Children Aged 19-35 Months. Maryland, National Immunization Survey.