National, State, and Local Area Vaccination Coverage Among Children Aged 19–35 Months — United States, 2011

High vaccination coverage in children by age 2 years has resulted in historically low levels of most vaccine-preventable diseases in the United States (1), but coverage must be maintained to reduce the burden of disease further and prevent a resurgence of these diseases, particularly in populations with lower vaccination coverage. This report describes national, state, and selected local area vaccination coverage by age 19–35 months for children born during January 2008–May 2010, based on 2011 National Immunization Survey (NIS) results. Vaccination coverage remained above the national Healthy People 2020 target* of 90% for ≥1 dose measles, mumps, rubella vaccine (MMR) (91.6%), ≥3 doses of hepatitis B vaccine (HepB) (91.1%), ≥3 doses of poliovirus vaccine (93.9%), and ≥1 dose of varicella vaccine (90.8%). For the birth dose of HepB, coverage increased from 64.1% in 2010 to 68.6% in 2011; for the more recently recommended ≥2 doses of hepatitis A vaccine (HepA) and rotavirus vaccines, coverage increased from 49.7% to 52.2% and from 59.2% to 67.3%, respectively; and for the full series of Haemophilus influenzae type b vaccine (Hib), coverage increased from 66.8% to 80.4%, reflecting recovery from the Hib shortage that occurred during December 2007–September 2009 (2). The percentage of children who had not received any vaccinations remained at <1%. Children living below the poverty level had lower coverage than children living at or above poverty for ≥4 doses of diphtheria, tetanus toxoid, and acellular pertussis vaccine (DTaP) and ≥4 doses of pneumococcal conjugate vaccine (PCV) (by 6 percentage points each); the full Hib series (by 8 percentage points); and for rotavirus vaccination (by 10 percentage points). Continued partnerships among national, state, local, private, and public entities are needed to sustain current coverage levels and ensure that coverage for the more recently recommended vaccines continues to increase for all children.

NIS uses a quarterly, random-digit–dialed sample of telephone numbers to reach households with children aged 19–35 months in the 50 states and selected local areas and territories,† followed by a mail survey sent to 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 and mixed telephone use (landline and cellular), household nonresponse, and exclusion of households without telephone service.§ Beginning in 2011, surveys included landline and cellular telephone households.¶ During 2011, the response rate** was 61.7% for the landline telephone sample and 25.2% for the cellular telephone sample. Providers returned adequate vaccination records for 71.6% of children with completed household interviews, for a total of 19,534 children with provider-reported vaccination records included in this report: 17,309 from the landline sampling frame and 2,225 from the cellular telephone sampling frame. Because the number of Hib†† and rotavirus vaccine§§ doses required differs according to manufacturer, coverage estimates for these vaccines take into account the type of vaccine used. Logistic regression was used to examine differences among racial/ethnic groups, controlling for poverty status, and to test for significant interactions between race/ethnicity and poverty status. Statistical analyses were conducted using t-tests based on weighted data and accounting for the complex survey design. A p-value of <0.05 was considered statistically significant.

From 2010 to 2011, national vaccination coverage increased from 66.8% to 80.4% for the full series of Hib, from 64.1% to 68.6% for the birth dose of HepB, from 49.7% to 52.2% for ≥2 doses of HepA, and from 59.2% to 67.3% for rotavirus vaccine (Table 1). For vaccines recommended before the inception of the NIS in 1994, coverage has remained stable since the mid-1990s,¶¶ with 2011 levels of 91.6% for ≥1 dose of MMR, 84.6% for ≥4 doses of DTaP, 91.1% for ≥3 doses of HepB, 90.8% for ≥1 dose of varicella vaccine, and 93.9% for ≥3 doses of poliovirus vaccine. Coverage with ≥4 doses of PCV was 84.4% in 2011, similar to coverage in 2010. As in 2009 and 2010, the seven-vaccine series (4:3:1:3:3:1:4)*** reported in 2011 excluded Hib because of the Hib shortage that occurred during December 2007–September 2009 (2). Coverage with the seven-vaccine series, excluding Hib, was 73.6% in 2011, similar to coverage in 2010. However, coverage with the seven-vaccine series (4:3:1:3*:3:1:4)††† that included the full series of Hib increased from 56.6% in 2010 to 68.5% in 2011 (Table 1).

Children living below the poverty level§§§ had lower coverage than children living at or above the poverty level for ≥3 doses of DTaP, ≥4 doses of DTaP, primary and full series of Hib, ≥4 doses of PCV, rotavirus vaccine, and the seven-vaccine series (including and excluding Hib) (Table 2). Children living below the poverty level had higher HepB birth dose coverage than children living at or above the poverty level. No differences by poverty status were observed for poliovirus vaccine, MMR, ≥3 doses of HepB, varicella vaccine, ≥3 doses of PCV, or ≥2 doses of HepA.

Compared with white children,¶¶¶ black children had lower coverage for ≥4 doses of DTaP, the full series of Hib, ≥4 doses of PCV, rotavirus vaccine, and the complete 4:3:1:3*:3:1:4 series (Table 2). However, the association of race with coverage did not persist after adjustment for poverty status. American Indian/Alaska Native (AI/AN) children had lower coverage for ≥4 doses of DTaP and ≥4 doses of PCV compared with white children. These differences remained after adjustment for poverty status. Black children and AI/AN children had higher HepB birth dose coverage than white children, which remained significant after adjustment for poverty. In unadjusted analyses, Hispanic children had higher coverage than white children for the birth dose of HepB, varicella vaccine, and ≥2 doses of HepA. However, differences in coverage between Hispanic and white children varied by poverty status, with Hispanic children having higher coverage compared with white children only among those children living below the poverty level for ≥4 doses of DTaP (84.2% for Hispanic children compared with 78.6% for white children), the full series of Hib (80.7% compared with 71.7%), ≥4 doses of PCV (84.1% compared with 77.5.%), ≥2 doses of HepA (57.8% compared with 45.0%), and rotavirus vaccine (66.1% compared with 57.4%). The observed difference in coverage between Hispanic and white children for varicella vaccine existed for children on both sides of the poverty line; the difference in coverage for the birth dose if HepB was no longer observed after adjustment for poverty status. Coverage was higher for Asian children compared with white children, independent of poverty status, for ≥3 doses of DTaP, ≥4 doses of DTaP, poliovirus vaccine, ≥3 doses of HepB, and varicella vaccine. Asian children had higher full Hib series coverage than white children only among children living below the poverty level (81.5% for Asian children compared with 71.7% for white children). All other observed differences in coverage between Hispanic and Asian children and white children did not persist after adjustment for poverty.

Vaccination coverage varied by state, with the largest variations for the birth dose of HepB and the more recently recommended vaccinations of HepA and rotavirus (Table 3). HepB birth dose coverage ranged from 23.1% in Vermont to 83.4% in Indiana and North Dakota, ≥2 doses of HepA coverage ranged from 29.3% in South Dakota to 69.2% in Nebraska, and rotavirus vaccine coverage ranged from 52.2% in Wyoming to 80.0% in Massachusetts. Although state-specific coverage was less variable for vaccines with longer-standing recommendations (e.g., MMR and DTaP), 15 states had coverage below the Healthy People 2020 objective of 90% for MMR vaccine, and only two states (Nebraska and Hawaii) had coverage ≥90% for ≥4 doses of DTaP.

Reported by

Carla L. Black, PhD, David Yankey, MS, Maureen Kolasa, MPH, Immunization Svcs Div, National Center for Immunization and Respiratory Diseases, CDC. Corresponding contributor: Carla L. Black, cblack2@cdc.gov, 404-639-8436.

Editorial Note

The results of the 2011 NIS indicate that vaccination coverage among children aged 19–35 months remained stable or increased compared with 2010 for all recommended vaccines. Coverage continued to meet or exceed national Healthy People 2020 objectives of 90% for MMR, HepB, poliovirus, and varicella vaccine. Coverage with the full series of Hib increased 13.6 percentage points compared with 2010. This increase likely reflects a recovery from the effect of the recommendation to defer the booster Hib dose during the Hib shortage that occurred during December 2007–June 2009 (2,3).

Coverage continued to increase for the more recently recommended vaccinations, including HepA and rotavirus, and the birth dose of HepB. PCV reached coverage levels comparable to those for DTaP, a vaccine that also requires 4 doses but with longer-standing recommendations. Although coverage did not yet reach the Healthy People 2020 objectives for these vaccines, the reduction in disease already has been substantial. Incidence of hepatitis A in the United States has decreased an estimated 93% relative to the prevaccine era (1). Hospitalizations associated with rotavirus infection among infants and young children have decreased 66%–89% (4,5). Although coverage with ≥4 doses PCV is not yet at 90%, the incidence of invasive pneumococcal disease in children <5 years caused by the serotypes of Streptococcus pneumoniae contained in the heptavalent PCV had decreased by 99% by 2007 (6). Incidence of all invasive pneumococcal disease is expected to decrease even further since the introduction of the 13-valent PCV in 2010.

Coverage for many vaccines differs by poverty level. Although the Vaccines For Children program**** has been successful in eliminating differences in coverage between children living above and below the poverty level that once existed for vaccines such as MMR, polio, and HepB (7), coverage among children living below poverty still lags behind coverage of children living at or above poverty for newer vaccines and vaccines that require 4 doses to complete the series.

Few differences by racial/ethnic group were observed after adjustment for poverty status. Differences in coverage between white and black children could be explained by a higher prevalence of poverty among black children. AI/AN children had lower coverage compared with white children for many vaccines, which could not be explained by other, readily apparent factors such as poverty or the introduction of the cellular telephone sampling frame. Coverage among AI/AN children decreased from 81.8% in 2010 to 72.7% in 2011 for ≥4 doses of DTaP, and from 85.3% to 75.3% for ≥4 doses of PCV. Because of a relatively small sample size for AI/AN children, differences could be attributable to random variation in the sample. Coverage among children in all other racial/ethnic groups was similar to or higher than coverage among white children for most vaccines.

Vaccination coverage continues to vary across states. Although coverage remains high nationally for many vaccines, clusters of unvaccinated children in geographically localized areas leave communities vulnerable to outbreaks of disease. Fifteen states have MMR coverage below 90%. The recent increases in measles outbreaks in the United States (8) underscore the importance of maintaining uniformly high coverage to protect from importation and transmission of disease.

The findings in this report are subject to at least four limitations. First, this was the first year that the NIS used a dual-frame sampling scheme that included landline and cellular telephone households. Estimates might not be comparable with those from previous years when surveys were conducted only via landline telephone. Although differences between national landline and dual-frame estimates for specific vaccines in the 2011 NIS were small, with absolute magnitude <1%, larger variations were observed for state-specific coverage estimates. Comparisons of 2011 estimates with those of previous years at the state level should be interpreted with caution. Second, underestimates of vaccination coverage might have resulted from the exclusive use of provider-reported vaccination histories because completeness of these records is unknown, and estimates might have been biased upwards or downwards if coverage among children for whom provider records were not returned differed from coverage among children with adequate provider data. Third, bias resulting from nonresponse and exclusion of households without telephone service might persist after weighting adjustments. Finally, although national coverage estimates are precise, estimates for state and local areas should be interpreted with caution because of smaller sample sizes and wider confidence intervals.

Most vaccine-preventable diseases have declined to historically low levels in the United States as a result of high vaccination coverage among preschool-aged children (1). Careful monitoring of coverage levels overall and in subpopulations (e.g., by race/ethnicity and by geographic area) is important to ensure that all children remain adequately protected. Many states can supplement NIS estimates with use of immunization information systems to track vaccination coverage at the community level. The results of the 2011 NIS indicate that coverage among young children has remained stable for vaccines with long-standing recommendations and continues to increase for more recently recommended vaccines. CDC encourages the use of evidence-based methods for improving and sustaining coverage, including components such as parent and provider reminders, reducing out-of-pocket costs, standing orders, home visits to vulnerable populations, vaccination requirements for child care centers, use of immunization information systems, and vaccination programs in child care centers and Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) settings†††† (9). Health insurance reforms of the Affordable Care Act require health plans to cover recommended immunizations without cost to the enrollee when administered by an in-network provider (10).

References

1. CDC. Vaccine-preventable diseases, immunizations, and MMWR—1961–2011. MMWR 2011;60(Suppl 4):49–57.
2. CDC. Interim recommendations for the use of Haemophilus influenzae type b (Hib) conjugate vaccines related to the recall of certain lots of Hib-containing vaccines (PadvaxHIB and Comvax). MMWR 2007;56:1318–20.
3. CDC. Updated recommendations for use of Haemophilus influenzae type b (Hib) vaccine: reinstatement of the booster dose at ages 12–15 months. MMWR 2009;58:673–4.
4. Yen C, Tate JE, Wenk JD, Harris M, Parashar UD. Diarrhea-associated hospitalizations among US children over 2 rotavirus seasons after vaccine introduction. Pediatrics 2011;127:e9–15.
5. Payne DC, Staat MA, Edwards KM, et al. Direct and indirect effects of rotavirus vaccination upon childhood hospitalizations in 3 US counties, 2006–2009. Clin Infect Dis 2011;53:245–53.
6. Tan TQ. Pediatric invasive pneumococcal disease in the United States in the era of pneumococcal conjugate vaccines. Clin Microbiol Rev 2012;25:409–18.
7. CDC. Vaccination coverage by race/ethnicity and poverty level among children aged 19–35 months—United States, 1996. MMWR 1997;46:963–8.
8. CDC. Measles—United States, 2011. MMWR 2012;61:253–7.
9. Community Preventive Services Task Force. The guide to community preventive services. Atlanta, GA: Community Preventive Services Task Force; 2011. Available at http://www.thecommunityguide.org/vaccines/universally/index.html. Accessed July 25, 2012.
10. Patient Protection and Affordable Care Act. Pub. L. No. 111-48,124 Stat. 119 (2010).