National and State Vaccination Coverage Among Children Aged 19--35 Months --- United States, 2010

The National Immunization Survey (NIS) monitors vaccination coverage among children aged 19--35 months using a random-digit--dialed sample of telephone numbers of households to evaluate childhood immunization programs in the United States. This report describes the 2010 NIS coverage estimates for children born during January 2007--July 2009. Nationally, vaccination coverage increased in 2010 compared with 2009 for ≥1 dose of measles, mumps, and rubella vaccine (MMR), from 90.0% to 91.5%; ≥4 doses of pneumococcal conjugate vaccine (PCV), from 80.4% to 83.3%; the birth dose of hepatitis B vaccine (HepB), from 60.8% to 64.1%; ≥2 doses of hepatitis A vaccine (HepA), from 46.6% to 49.7%; rotavirus vaccine, from 43.9% to 59.2%; and the full series of Haemophilus influenzae type b (Hib) vaccine, from 54.8% to 66.8%. Coverage for poliovirus vaccine (93.3%), MMR (91.5%), ≥3 doses HepB (91.8%), and varicella vaccine (90.4%) continued to be at or above the national health objective targets of 90% for these vaccines.* The percentage of children who had not received any vaccinations remained low (<1%). For most vaccines, no disparities by racial/ethnic group were observed, with coverage for other racial/ethnic groups in 2010 similar to or higher than coverage among white children. However, disparities by poverty status still exist. 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 (1).

NIS uses a quarterly, random-digit--dialed sample of telephone numbers to reach households with children aged 19--35 months for the 50 states and selected local areas and territories,† followed by a mail survey 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, household nonresponse, and exclusion of households without landline telephones.§ During 2010, the household response rate¶ was 63.8%; providers returned vaccination records for 71.2% of all children with completed household interviews, for a total of 17,004 children with provider-reported vaccination records included in this report. Because the number of Hib** vaccine and rotavirus†† vaccine doses required differs according to manufacturer, coverage estimates for these vaccines take into account 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. A p-value of <0.05 was considered statistically significant.

During 2010, national coverage with all recommended vaccines increased or remained stable compared with 2009 (Table 1). Coverage with vaccines with longstanding recommendations has remained stable since the mid-1990s§§ (i.e., diphtheria, tetanus toxoids, and acellular pertussis vaccine [DTaP], poliovirus vaccine, varicella vaccine, and ≥3 doses of HepB). For MMR, after a decrease from 92.1 in 2008 to 90.0 in 2009, coverage with ≥1 dose increased to 91.5% in 2010. Although coverage with the primary series of Hib vaccine remained stable at 92.2%, coverage with the full series (primary series plus booster dose) increased to 66.8% in 2010 from 54.8% in 2009. For the most recently recommended vaccinations, coverage with rotavirus vaccine increased to 59.2% in 2010 from 43.9% in 2009. Within the 2010 sample, rotavirus vaccination coverage increased from 51.9% among children born during January--June 2007 to 69.8% among children born during January--June 2009. Coverage with ≥2 doses of HepA increased to 49.7% in 2010 from 46.6% in 2009, coverage with the first dose of HepB within 3 days of birth (birth dose) increased to 64.1% in 2010 from 60.8% in 2009, and coverage with ≥4 doses of PCV increased to 83.3% in 2010 from 80.4% in 2009. As in 2009, the seven-vaccine series (4:3:1:3:3:1:4)¶¶ reported in 2010 excludes the Hib vaccine because of the Hib vaccine shortage that occurred during December 2007--September 2009 (2,3). Coverage with the modified seven-vaccine series (excluding Hib vaccine) increased to 72.7% in 2010 from 70.5% in 2009 (Table 1).

Coverage varied by race/ethnicity.*** Among black children, coverage with ≥4 doses of PCV and rotavirus vaccine was lower compared with white children (Table 2). Compared with white children, coverage with ≥1 dose of varicella vaccine was higher among black, Hispanic, American Indian/Alaska Native, and Asian children. Also compared with white children, coverage among Hispanic children was higher for ≥1 dose of MMR and ≥2 doses of HepA, and coverage among American Indian/Alaska Native children was higher for the primary and full series of Hib vaccine and ≥3 doses of HepB. With the exception of the difference in coverage between white children and black children for ≥4 doses of PCV, all differences remained statistically significant after controlling for poverty status.

Coverage among children living below poverty level††† was lower than coverage among children living at or above poverty level for ≥3 and ≥4 doses DTaP, the primary and full series of the Hib vaccine, ≥3 and ≥4 doses PCV, rotavirus vaccine, and the 4:3:1:3:3:1:4 series with and without Hib (Table 2). Coverage with the birth dose of HepB was higher among children living below the poverty level compared with children living at or above the poverty level.

Vaccination coverage continued to vary by state, particularly for the more recently recommended vaccinations (Table 3). Coverage with rotavirus vaccine in 2010 significantly increased in 40 states compared with 2009, and coverage ranged from 42.1% in Maine to 82.1% in Delaware. Coverage with ≥2 doses HepA significantly increased in six states compared with 2009, and ranged from 27.2% in Maine to 64.4% in Georgia. Coverage with the birth dose of HepB significantly increased in five states compared with 2009, and ranged from 21.4% in Vermont to 83.3% in Kentucky. Coverage with MMR was greater than 85% in all states. Coverage for the modified vaccine series (4:3:1:3:3:1:4 series excluding Hib) varied by state, from 61.3% in Nevada to 82.7% in Wisconsin.

Reported by

Carla L. Black, PhD, Karen G. Wooten, MA, 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 2010 NIS indicate that vaccination coverage among children aged 19--35 months remained stable or increased compared with 2009. Coverage levels for poliovirus vaccine, MMR, HepB, and varicella vaccine continue to be at or above 90%, the national health objective target for these vaccines. The record high number of measles cases reported in the United States so far in 2011 (4) underscores the importance of maintaining high MMR coverage to protect from measles importations and transmission in the United States. Nevertheless, room for improvement exists. Nearly one in 10 children has not received MMR by age 19--35 months.

Among the more recently recommended vaccines, coverage continued to increase for ≥4 doses PCV, the birth dose of HepB, and HepA. Coverage with rotavirus vaccine increased 15.3 percentage points, from 43.9% in 2009 to 59.2% in 2010. Although some children in the 2009 NIS sample were born before the 2006 introduction of live rotavirus vaccine and thus were not affected by the recommendation to be vaccinated, the large increase in coverage observed in the 2010 NIS and the trend in increased coverage among successive birth cohorts within the 2010 sample indicate that the recommendation for rotavirus vaccination was successfully implemented in more recent birth cohorts, and coverage likely will continue to increase.

Coverage with the primary series of Hib vaccine remained stable at 92.2%, indicating that during the shortage of Hib vaccine that occurred during December 2007--June 2009, vaccination providers were able to comply with the interim recommendations to defer the booster dose but continue to vaccinate children with the primary series (2). Children in both the 2009 and 2010 NIS samples were affected by the temporary recommendation to suspend the booster dose of Hib vaccine. Coverage with the full series of Hib vaccine increased by 12 percentage points in 2010 compared with 2009, suggesting that children received the booster dose as Hib vaccine supplies became adequate starting in July 2009 (3).

In the 2009 NIS, disparities in coverage between white children and children of other racial/ethnic groups were reported for several of the recommended vaccines (e.g., HepA, PCV, and DTaP) (5). Because of increases in coverage among minority children, the 2010 coverage levels for most vaccines among other racial/ethnic groups were similar to or higher than coverage levels among white children; however, racial/ethnic disparities independent of poverty still remained for rotavirus. Disparities in coverage by poverty level remained for many vaccines. Although 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, the remaining disparities in coverage by poverty status reflect barriers to vaccination that must be addressed.

Vaccination coverage continues to vary across states, especially for the more recently recommended vaccines. Differences by state in factors such as population characteristics, state policies (e.g., child-care vaccination requirements), vaccine financing policies that affect the availability of publicly purchased vaccine, and immunization program activities (e.g., the presence of outreach activities) likely contribute to variations in vaccination coverage (6,7). Further work is needed to understand factors that most strongly influence vaccination coverage and 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 telephones. Previous studies have shown that vaccination coverage estimates that include nonlandline households might be lower than NIS estimates (8). During the fourth quarter, the 2010 NIS sampled telephone numbers from a cellular telephone sampling frame.¶¶¶ Differences between national landline and dual-frame (including households interviewed by landline plus those from the cellular telephone sampling frame) coverage estimates for specific vaccines and series ranged from -1.2 to 2.2 percentage points. 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, estimates for state and local areas should be interpreted with caution because of smaller sample sizes and wider confidence intervals.

A recent economic analysis of the United States immunization policy indicated that vaccination of each U.S. birth cohort with the current childhood immunization schedule prevents approximately 42,000 deaths and 20 million cases of disease, with net savings of nearly $14 billion in direct costs and $69 billion in total societal costs (1). Although coverage levels for more recently recommended vaccines have continued to increase, the careful monitoring of coverage levels overall and in subpopulations (e.g., by race/ethnicity and geographic area) will be important to ensure that all children are adequately protected. The results of the 2010 NIS indicate that parents and primary-care givers continued to ensure that children were vaccinated, despite temporary suspension of the booster dose of Hib vaccine during 2007--2009 because of a national vaccine shortage (4), heightened public concerns regarding vaccine safety (9), and budget challenges experienced by states (10). The Guide to Community Preventive Services recognizes the effectiveness of continued partnerships among national, state, local, private, and public entities in sustaining vaccination coverage levels and ensuring that coverage levels for the more recently recommended vaccines continue to increase.****

References

1. CDC. Ten great public health achievements---United States, 2001--2010. MMWR 2011;60:619--23.
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. 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. CDC. Measles---United States, January--May 20, 2011. MMWR 2011;60:666--8.
5. CDC. National, state, and local area vaccination coverage among children aged 19--35 months---United States, 2009. MMWR 2010;59:1171--7.
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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. 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.
9. Chatterjee A, O'Keefe C. Current controversies in the USA regarding vaccine safety. Expert Rev Vaccines 2010;9:497--502.
10. Association of State and Territorial Health Officials. Budget cuts continue to affect the health of Americans: update May 2011. Available at http://www.astho.org/display/assetdisplay.aspx?id=6024. Accessed August 24, 2011.