National, State, and Local Area Vaccination Coverage Among Children Aged 19--35 Months --- United States, 2009

Since 1994, the National Immunization Survey (NIS) has been collecting data to monitor childhood immunization coverage. This report describes the 2009 NIS coverage estimates for children born during January 2006--July 2008 and focuses on the more recently recommended vaccines (i.e., hepatitis B [HepB] vaccine birth dose, hepatitis A vaccine [HepA], pneumococcal conjugate vaccine [PCV], and rotavirus vaccine) for children aged 19--35 months. The most recent NIS data indicate that vaccination coverage increased in 2009 compared with 2008 for HepB birth dose (from 55.3% to 60.8%) and HepA (from 40.4% to 46.6%), but coverage for PCV (≥4 doses) remained stable (80.4%). Full coverage for rotavirus vaccine was 43.9% among children born within 2 years of licensure (1). Coverage for poliovirus (92.8%), measles, mumps, and rubella (MMR) (90.0%), hepatitis B (HepB) (92.4%), and varicella (VAR) (89.6%) vaccines continued to be at or near the national health objective of 90%, although coverage for MMR and HepB vaccines decreased slightly in 2009. The percentage of children who have not received any vaccines remained low (<1%). Parents and primary-care providers continued to ensure that children were vaccinated, in spite of interim recommendations to suspend the booster dose of Haemophilus influenzae type b vaccine (Hib) because of a national shortage, and heightened public awareness of controversies in vaccine safety (2,3).

To estimate coverage for all age-eligible children, NIS uses a quarterly, random-digit--dialed sample of telephone numbers for the 50 states and selected urban areas and territories,* followed by a mail survey of the children's vaccination providers to collect vaccination information. Data were weighted to represent the population of children aged 19--35 months, with adjustments for households with multiple telephone lines, household nonresponse, and exclusion of households without landline telephones.† During 2009, the household response rate§ was 63.9%; a total of 17,313 children with provider-reported vaccination records were included in this report, representing 70.7% of all children with completed household interviews. Because the number of Hib¶ and rotavirus** vaccine doses required differs according to manufacturer, coverage estimates for these vaccines now take into account the brand of vaccine used. Logistic regression was used to examine differences among racial/ethnic groups, controlling for poverty status. Statistical analyses were conducted using t-tests based on weighted data and accounting for the complex survey design. All tests with p<0.05 were regarded as statistically significant.

During 2009, national coverage with the first dose of HepB within 3 days of birth (birth dose) increased to 60.8% from 55.3% in 2008, the largest increase observed for the birth dose in the past 5 years (Table 1); by state, coverage ranged from 22.8% in Vermont to 80.7% in Michigan (Table 2). Coverage with ≥2 doses of HepA vaccine increased from 40.4% in 2008 to 46.6% in 2009. Coverage ranged from 19.3% in Maine to 63.2% in North Dakota. Coverage with ≥4 doses PCV at the national level changed little (from 80.1% to 80.4%), but increased significantly in Illinois (from 76.2% to 82.9%), Mississippi (from 74.7% to 85.0%), Nevada (from 63.6% to 75.1%), and Wyoming (from 69.2% to 82.3%). Across all states, PCV coverage ranged from 67.5% in Missouri to 90.7% in Connecticut. Coverage for rotavirus vaccine was 43.9% nationally, similar to previous coverage reports for newly recommended vaccines, and varied widely by state, from 20.9% in Washington to 71.2% in Rhode Island. Rotavirus vaccine coverage increased from 8.0% among children born during January--June 2006 to 60.0% among children born January--June 2008. For children born between those periods, estimated coverage ranged from 34.8% for children born July--December 2006, to 49.0% for children born January--June 2007, to 53.4% for children born July--December 2007.

The seven-vaccine series (i.e., 4:3:1:3:3:1:4) reported in the 2009 NIS added ≥4 doses of PCV to the combined 4:3:1:3:3:1†† series reported in previous years. Because of changes in measurement of the Hib vaccine and the vaccine shortage that occurred from December 2007 to September 2009 (2), state coverage estimates included in this report were based on the series that excludes Hib. Using this modified seven-vaccine series (minus Hib), coverage remained stable in 2009 (70.5%) compared with 2008 (70.6%) (Table 1). In 2009, modified series coverage ranged from 56.2% in Missouri to 78.1% in Iowa (Table 2). Significant increases were observed in Wyoming (69.6% versus 58.9%), Idaho (70.5% versus 60.4%), Oklahoma (66.3% versus 57.4%), Nevada (62.6% versus 55.2%), and North Dakota (77.0% versus 69.1%). Among the 13 local areas, coverage ranged from 61.4% in the eastern/western counties of Washington to 73.5% in Los Angeles, California. The percentage of children aged 19--35 months receiving no vaccinations remained at 0.6%.

Coverage differed by race/ethnicity.§§ Among the more recently recommended vaccines, PCV and rotavirus coverage was lower among black and multiracial children than among white children (Table 3). Coverage for PCV also was lower among Asian children. Coverage for HepA was lower among black children and American Indian/Alaska Native children than among white children. Except for rotavirus coverage among black children, these differences persisted after controlling for poverty status. HepB birth dose coverage was higher among Hispanic children than among white children. For vaccines with longer-standing recommendations, differences were observed for diphtheria, tetanus toxoid, and acellular pertussis (DTaP) vaccine. Compared with coverage among white children, coverage was lower for black children for ≥3 and ≥4 DTaP doses and lower for Hispanic children for ≥4 doses only. The difference in coverage between white and black children for ≥4 doses remained statistically significant after controlling for poverty status.

Coverage also differed by poverty status.¶¶ Coverage for HepB birth dose was higher among children living below poverty level than for those living at or above poverty level (by 3.8 percentage points). Among children living below poverty level, coverage was lower for ≥4 doses of PCV (by 8.4 percentage points) and rotavirus vaccine (by 9.4 percentage points) than for other children. Among the longer-standing recommendations, coverage for ≥4 doses of DTaP also was lower (by 5.6 percentage points).

Reported by

KG Wooten, MA, M Kolasa, MPH, JA Singleton MS, A Shefer, MD, Immunization Svcs Div, National Center for Immunization and Respiratory Diseases, CDC.

Editorial Note

NIS is the only population-based survey to provide national, state, local area, and territorial estimates of provider-reported vaccination coverage among children aged 19--35 months in the United States. Coverage levels for poliovirus, MMR, HepB, and VAR continued to hold at or above 90%, the national health objective for specific vaccines. PCV, first recommended in 2000, has now reached coverage levels comparable to those for DTaP, a vaccine also requiring 4 doses but with longer-standing recommendations. For the more recently recommended vaccines, coverage for the birth dose of the HepB series and the full series of HepA increased. These findings demonstrate the ability of immunization programs at state and local levels to incorporate newly recommended vaccines while sustaining coverage at or above national target levels for most longer-standing recommended vaccines. Careful monitoring of uptake of new vaccines overall and in subpopulations (e.g., by race/ethnicity and geographically) will be important to ensure that all children are protected adequately against vaccine-preventable diseases.

The Hib shortage and interim recommendation to suspend the booster dose for healthy children (2) occurred during a period when 70% of the children in the 2009 NIS would have been eligible for the booster dose of Hib vaccine. Not surprisingly, Hib vaccine coverage measured by receipt of ≥3 doses dropped from 90.9% in 2008 to 83.6% in 2009, in part because of the shortage and interim recommendation. Starting in 2009, coverage estimates are reported based on a more accurate measurement of Hib vaccination status that takes into account vaccine product type (Hib vaccine products vary in the number of recommended doses) (2). Concerns that providers were not vaccinating children adequately with the primary series during the shortage and temporary suspension of the booster vaccine proved unfounded; nationally, 92.1% of eligible children completed the primary series for Hib.

Since the 2006 introduction of live rotavirus vaccine, hospitalizations for gastroenteritis during the rotavirus season have declined markedly, beginning in 2007, as have emergency department and physician office visits for gastroenteritis (4). NIS estimates of rotavirus coverage in this report reflect early vaccinations, primarily among children born during the first 2 years of licensure of rotavirus vaccine. Analysis by birth cohort of the 2009 NIS showed rotavirus vaccination for the full vaccine series has increased steadily and reached 60.0% among children born during January--June 2008; overall vaccination coverage for rotavirus likely will continue to increase.

The Vaccines for Children program,*** a federal entitlement program that provides vaccine at no cost for eligible children, has been effective in reducing potential gaps in coverage levels resulting from poverty status; however, some gaps persist that reflect other barriers that must be addressed. Race/ethnicity was associated with vaccination status in the 2009 NIS data, independent of poverty status, for HepA, 4 doses of PCV, and 4 doses of DTaP. In the 2008 NIS data, racial/ethnic disparities for 4 doses of PCV and 4 doses of DTaP were observed but did not persist after controlling for poverty status (5). Associations of race/ethnicity and poverty with vaccination status will continue to be monitored, and further research will explore reasons for disparities.

State variation in vaccine coverage persists year to year. Many factors that potentially could affect vaccination coverage rates vary across states. Such factors include population characteristics, health system characteristics, state policies (e.g., child care vaccination requirements), vaccine financing policies that might affect speed with which new vaccine recommendations can be adopted and the degree to which underinsured children can receive publicly purchased vaccine, reimbursement of providers for immunization services, and immunization program activities (6--8). How these various factors interact to influence observed differences in vaccination coverage is unclear. Further work is needed to understand factors that most strongly influence vaccination coverage and to identify best practices among states.

The findings in this report are subject to at least three limitations. First, NIS is a landline-based telephone survey, and statistical adjustments might not fully compensate for nonresponse and households without landline or only cellular telephones. Vaccination coverage estimates that include nonlandline households might be lower than NIS estimates (9). Second, underestimates of vaccination coverage might have resulted from the exclusive use of provider-reported vaccination histories because completeness of these records is unknown. Finally, although national coverage estimates are precise, annual estimates and trends for state and local areas should be interpreted with caution because of smaller sample sizes and wider confidence intervals.

Achieving and maintaining high vaccination coverage levels is important to reduce the burden of vaccine-preventable diseases and prevent a resurgence of these diseases in the United States, particularly in undervaccinated populations. Continued partnerships among national, state, local, private, and public entities are needed to sustain vaccination coverage levels and ensure that coverage levels for the more recently recommended vaccines continue to increase. CDC encourages the use of evidence-based methods of improving coverage, which include parent and provider reminders, reducing out-of-pocket costs, increasing access to vaccination, and multicomponent interventions that include education (10). Research is under way to understand barriers to implementing proven methods of improving coverage and identify approaches to promoting more widespread implementation.

References

1. CDC. Reduction in rotavirus after vaccine introduction---United States, 2000--2009. MMWR 2009;48:1146--9.
2. CDC. Changes in measurement of Haemophilus influenzae serotype b (Hib) vaccination coverage---National Immunization Survey, United States, 2009. MMWR 2010;59:1069--72.
3. Chatterjee A, O'Keefe C. Current controversies in the USA regarding vaccine safety. Expert Rev Vaccines 2010;9:497--502.
4. Curns AT, Steiner CA, Barrett M, Hunter K, Wilson E, Parashar UD. Reduction in acute gastroenteritis hospitalizations among US children after introduction of rotavirus vaccine: analysis of hospital discharge data from 18 US states. J Infect Dis 2010;201:1607--10.
5. CDC. National, state, and local area vaccination coverage among children aged 19--35 months---United States, 2008. MMWR 2009;58:921--6.
6. Groom H, Kennedy A, Evans V, Fasano N. Qualitative analysis of immunization programs with most improved childhood vaccination coverage from 2001 to 2004. J Public Health Manag Pract 2010;16:E1--8.
7. Lee GM, Santoli JM, Hannan C, et al. Gaps in vaccine financing for underinsured children in the United States. JAMA 2007;298:638--43.
8. Coleman MS, Lindley MC, Ekong J, Rodewald L. Net financial gain or loss from vaccination in pediatric medical practices. Pediatrics 2009;124:S472--91.
9. Barron M, Wooten K, Taylor B. Comparing vaccination estimates from four survey designs: vaccination estimates from RDD, RDD+Cell, ABS, and area probability sampling. Presented at the 2010 Joint Statistical Meetings; July 31--August 5, 2010; Vancouver, British Columbia, Canada.
10. Task Force on Community Preventive Services. Recommendations regarding interventions to improve vaccination coverage in children, adolescents, and adults. Am J Prev Med 2000;18(1S):92--6.

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