Vaccination Coverage Among Children in Kindergarten --- United States, 2009--10 School Year

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Healthy People 2020 objectives include maintaining vaccination coverage among children in kindergarten (IID-10) (1). The target is ≥95% vaccination coverage for the following vaccines: poliovirus; diphtheria and tetanus toxoids and acellular pertussis (DTP/DTaP/DT); measles, mumps, and rubella (MMR); hepatitis B (HepB); and varicella (1). Data from school assessment surveys are used to monitor vaccination coverage and vaccination exemption levels among children enrolled in kindergarten. This report summarizes data from school assessment surveys submitted to CDC by 48 federal immunization program grantees (including 47 states and the District of Columbia) for the 2009--10 school year to describe vaccination coverage and exemption rates (2). For that period, 17 grantees reported coverage of ≥95% for four vaccines (poliovirus, DTP/DTaP/DT, MMR, and HepB) and four grantees reported coverage of ≥95% for 2 doses of varicella vaccine. Total exemption rates, including medical, religious, and philosophical exemptions, ranged from <1% to 6.2% across grantees, and 15 grantees reported exemption rates <1%. Survey methods for vaccination coverage and exemption rates varied among grantees, making comparisons difficult and limiting the use of school assessment surveys to report aggregate national rates. Further standardization of school assessment survey methods will generate comparable data between grantees to monitor and track progress in reaching national objectives, and allow development of best practice guidelines for grantees to more effectively use and report school coverage and exemption data. CDC will continue to monitor vaccination coverage and exemption levels and assist grantees in identification of local areas with low vaccination coverage or high exemption rates for further evaluation or intervention.

School vaccination requirements in the United States date back to 1855, when Massachusetts became the first state to require smallpox vaccine for school entry to control smallpox epidemics. The U.S. Supreme Court upheld the constitutionality of school vaccination requirements in 1922.* Since 1978, vaccination levels among children entering school have been assessed annually by state and local health departments. In general, school or health department personnel review the vaccination histories of enrolled students to determine compliance with school requirements established to protect children from vaccine-preventable diseases and ensure high vaccination coverage rates as they begin school. Results of the school-level reviews are reported to the state/area health department, which then reports aggregated totals to CDC; not all grantees report both vaccination coverage and exemption levels.

For the 2009--10 school year, vaccination coverage levels for children enrolled in kindergarten were available from 46 grantees. The number of children enrolled in kindergarten with an exemption for medical, religious, or philosophical reasons was available from 47 grantees. All of the reporting grantees assessed public schools, and all but North Dakota and Wisconsin included private schools in their assessment. Although 37 grantees assessed all schools with a kindergarten class, a smaller group (Delaware, Georgia, Hawaii, Missouri, Nevada, New Mexico, Rhode Island, South Carolina, Virginia, and Wisconsin) assessed a random sample of schools, and Alaska assessed a nonrandom sample of schools. For grantees that submitted reports for <95% of enrolled students, data were weighted based on population.

The vaccination status of students was considered up-to-date if they had received all of the vaccine doses required for school entry in their state or area. All reporting grantees require 3 or 4 doses of poliovirus vaccine and 2 doses of MMR vaccine. School entry requirements for other vaccinations vary by state/area: 44 grantees require 4 or 5 doses of DTP/DTaP/DT, 41 grantees require 3 doses of HepB vaccine, and 25 grantees require 1 dose and 18 grantees require 2 doses of varicella vaccine.† The types of exemptions and the process for obtaining exemptions also varied by grantee (3). All reporting grantees allowed medical exemptions, 43 allowed religious exemptions, and 16 allowed philosophical exemptions; two grantees (Mississippi and West Virginia) did not allow exemptions for religious or philosophical reasons. Exemption data reported to CDC are nonspecific and do not indicate whether the exemption was for one vaccine, a required vaccine dose, or for all required vaccines. Vaccination and exemption status also might not have been reported for each surveyed child because some children might have been in the process of obtaining required vaccines, as allowed by local policy.

Excluding varicella vaccine, the number of reporting grantees with ≥95% vaccination coverage ranged from 23 (50%) grantees for 2 doses of MMR vaccine to 28 (67%) grantees for HepB vaccine (Tables 1 and 2); 17 grantees achieved ≥95% coverage for four vaccines (complete series of poliovirus, DTP/DTaP/DT, MMR, and HepB vaccines). Among the 21 grantees that monitor receipt of 2 doses of varicella vaccine, coverage ranged from 62.9% (Idaho) to 99.6% (Georgia), with 10 grantees reporting coverage ≥90% and four grantees reporting coverage ≥95% (Table 2).

Total exemptions varied widely by grantee, ranging from <0.1% (Mississippi) to 6.2% (Washington); 15 grantees had a total exemption rate ≥3.0% (Table 3). Of the three types of allowable exemptions, medical exemptions were the least frequent, ranging from <0.1% (Mississippi) to 1.7% (Alaska). Nonmedical exemptions ranged from 0.2% (Rhode Island) to 5.8% (Washington) among the 45 grantees that allow nonmedical exemptions.

Reported by

Shannon Stokley, MPH, Carol Stanwyck, PhD, Bob Avey, Stacie Greby, DVM, Immunization Svcs Div, National Center for Immunization and Respiratory Diseases, CDC. Corresponding contributor: Shannon Stokley, sstokley@cdc.gov, 404-639-8734.

Editorial Note

Findings from this report showed that, in general, coverage rates for most recommended vaccines among children entering kindergarten were ≥90%; however, some grantees were below the Healthy People 2020 target of ≥95% coverage. Maintaining high MMR vaccination coverage rates, particularly among preschool children (>90% 1-dose coverage) and school-aged children (>95% 2-dose coverage), is essential to maintain measles elimination in the United States (4). However, only 50% of grantees reported that >95% of kindergartners surveyed had received 2 doses of MMR vaccine.

This is the first report of exemption data from the school assessment surveys. Overall exemption rates were low. Monitoring exemptions is important because several measles outbreaks in recent years occurred among school-aged children who were eligible for vaccination but whose parents chose not to have them vaccinated (5,6). For the majority of grantees, exemptions for medical reasons were <1%, and <3% for nonmedical reasons. Although the low exemption rates are reassuring, data in this report were aggregated at the grantee level, preventing analysis at the local or school level. Previous studies have shown that exemptions tend to cluster geographically and within schools (5,7); therefore, areas with high exemption levels might exist, even in states that have a low overall exemption rate, thereby creating pockets of undervaccinated children vulnerable to an outbreak of vaccine-preventable illness. Because reported exemptions do not distinguish between an exemption for one vaccine versus all vaccines, a student with a claimed exemption could have received one or more vaccines. Previous studies have found that exemptions to all vaccines are less common; a recent study of 277 children with nonmedical vaccine exemptions residing in four states found that 209 (75%) had received at least one vaccine (8). Additionally, vaccination coverage estimates from the 2009 National Immunization Survey showed that <1% of infants aged 19--35 months had not received any vaccines (9). Continued monitoring of exemption rates at the state and local school level will be important to determine if rates increase over time and to identify areas of undervaccination that will need evaluation or intervention.

The findings in this report are subject to at least three limitations. First, the variation of required vaccinations and assessment methods among kindergarten children across grantees and over time limits comparability of data. Second, data included in this report are a cross-sectional representation of vaccination coverage and exemption rates at one point in time; therefore, students who were in the process of obtaining required vaccines or claiming an exemption, as allowed by local policy, might not be accounted for in the reported estimates. Consequently, vaccination coverage and exemption rates might be underestimated for some grantees (the level of unaccounted for students ranges from 0% to 17.5%). Finally, the reasons why some parents seek vaccination exemptions could not be determined because reported data are limited.

CDC has been working with state immunization programs to 1) improve their school assessment survey methods to evaluate their vaccination programs, 2) identify local areas of undervaccinated children, and 3) standardize reporting of data to allow valid state comparisons and national estimates. For example, CDC has provided a standardized, online reporting system since the 2002--03 school year (2). CDC also is partnering with grantees to achieve greater standardization of reporting, including asking them to report coverage for a similar timeframe each year and report coverage based on Advisory Committee on Immunization Practices (ACIP) vaccination recommendations, in addition to reporting coverage based on state/area requirements. CDC has funded a national survey to assess state/area practices and will develop best practices for collecting and reporting vaccination coverage and exemption data.

School vaccination requirements are essential to protect kindergarten students from vaccine-preventable diseases and are recommended as an evidence-based strategy by the Task Force on Community Preventive Services to improve vaccination coverage levels (10). School vaccination assessments can identify pockets of undervaccination and help focus public health strategies where they can be most effective. This report underscores the need for standardized school assessment reporting to support public health activities, ensure valid comparisons of coverage rates across states, and develop valid national estimates to monitor progress toward achieving Healthy People 2020 objectives.

References

1. US Department of Health and Human Services. Healthy people 2020: immunization and infectious diseases. Washington, DC: US Department of Health and Human Services; 2010. Available at http://www.healthypeople.gov/2020/topicsobjectives2020/overview.aspx?topicId=23. Accessed May 26, 2011.
2. CDC. The school entry immunization assessment report, 2009--10. Atlanta, GA: US Department of Health and Human Services, CDC; 2010. Available at http://www.cdc.gov/vaccines/stats-surv/schoolsurv/default.htm. Accessed May 26, 2011.
3. Rota JS, Salmon DA, Rodewald LE, Chen RT, Hibbs BF, Gangarosa EJ. Processes for obtaining nonmedical exemptions to state immunization laws. Am J Public Health 2001;91:645--8.
4. Gay NJ. The theory of measles elimination: implications for the design of elimination strategies. J Infect Dis 2004;189(Suppl 1):S27--35.
5. Sugerman DE, Barskey AE, Delea MG, et al. Measles outbreak in a highly vaccinated population, San Diego, 2008: role of the intentionally undervaccinated. Pediatrics 2010;125:747--55.
6. CDC. Update: measles---United States, January--July 2008. MMWR 2008;57:893--6.
7. Omer SB, Enger KS, Moulton LH, Halsey NA, Stokley S, Salmon DA. Geographic clustering of nonmedical exemptions to school immunization requirements and associations with geographic clustering of pertussis. Am J Epidemiol 2008;168:1389--96.
8. Salmon DA, Moulton LH, Omer SB, deHart MP, Stokley S, Halsey NA. Factors associated with refusal of childhood vaccines among parents of school-aged children. Arch Pediatr Adolesc Med 2005;159:470--6.
9. CDC. National, state, and local area vaccination coverage among children aged 19--35 months---United States, 2009. MMWR 2010;59:1171--77.
10. CDC. Vaccinations to prevent diseases: universally recommended vaccinations. In: Guide to community preventive services. Atlanta, GA: US Department of Health and Human Services, CDC; 2011. Available at http://www.thecommunityguide.org/vaccines/universally/index.html. Accessed April 13, 2011.