Vaccination Coverage among Children Enrolled in Kindergarten in the U.S. Virgin Islands

Background:
Annually, U.S. states and territories assess vaccination coverage rates at school entry in order to monitor disease risk and compliance with school entry requirements. Working with CDC, the Virgin Islands designed an assessment methodology to determine whether there were pockets of unvaccinated children entering school. Based on programmatic experiences, efforts were focused on detecting differences between public and private schools and by island (St. John, St. Thomas, and St. Croix).

Objectives:
The objectives of this survey were to 1) evaluate compliance with Virgin Island school entry requirements, and 2) determine whether there were significant differences in coverage rates by school type or geography.

Methods:
A random sample, stratified by school type and geography, was selected using probability proportional to size of school. During the 2007-2008 school year, staff members from the Virgin Island health department reviewed vaccination records of enrolled kindergarten students (n = 700) in each school in the sample.

Results:
For each vaccine assessed (DTaP, Polio, MMR, HepB, and varicella), the percentage of kindergarteners that were up-to-date (UTD) differed significantly by school type and by island. For instance, the percentage of kindergarteners that had 4+ doses of DTaP at school entry was 68.02% for private schools and 89.00% for public schools (X2 = 44.69, p<.0001). Similarly, the percentage of kindergarteners with 4+ DTaP was 96.36% for St. John, 88.43% for St. Croix, and 76.32% for St. Thomas (X2 = 26.83, p<.0001) . Similar patterns by school type and island were found for each of the other vaccines.

Conclusions:
When assessing school vaccination coverage rates it is important to consider subgroups within the population in order to determine whether there are children who are undervaccinated and therefore at greater risk for VPDs. Testing for differences between subgroups can provide valuable information and allow for the development of targeted interventions to increase vaccine coverage.