Interim Results: State-Specific Influenza Vaccination Coverage --- United States, August 2010--February 2011

The 2010--11 influenza season was unusual because it followed the 2009 influenza A pandemic (H1N1) season and it was the first season the Advisory Committee on Immunization Practices (ACIP) recommended influenza vaccination of all persons aged ≥6 months (1). The season also was notable because a record number of seasonal influenza vaccine doses (approximately 163 million) were distributed in the United States (2). To provide preliminary state-specific influenza vaccination coverage estimates, CDC analyzed Behavioral Risk Factor Surveillance System (BRFSS) data for adults aged ≥18 years and National Immunization Survey (NIS) data for children aged 6 months--17 years collected September 2010 through March 2011. By February 28, the preliminary national vaccination coverage estimate was 49.0% for children aged 6 months--17 years; among 43 states and the District of Columbia (DC), coverage ranged from 30.2% for adults aged 18--49 years to 68.6% for adults aged ≥65 years. The record high seasonal vaccination coverage achieved during 2009--10 (41.3%) among persons aged ≥6 months in 43 states and DC was sustained during the 2010--11 season (42.8%). Coverage for Hispanic and non-Hispanic black children increased by 11--12 percentage points from 2009--10 levels. Opportunity exists to improve coverage in all age groups, particularly among adults. To accomplish that, health departments and other nonoffice-based vaccination providers can increase access to vaccination at work and school locations, pharmacies and stores, and other nonmedical sites. In addition, physicians and clinics should implement proven strategies for improving vaccination coverage (e.g., office-based protocols, including reminder/recall notification and standing orders) (3).

CDC analyzed data collected September 2010--March 2011 from 43 states and DC for BRFSS and from all 50 states and DC for NIS. BRFSS respondents aged ≥18 years were asked if they had received an influenza vaccination in the past 12 months, and if so, in which month.* NIS respondents aged ≥18 years were asked whether their children had received an influenza vaccination since August, and if so, in which month.† The median state Council of American Survey and Research Organizations (CASRO) BRFSS response rate was 54.4% during the data collection timeframe. The NIS CASRO quarterly response rates ranged from 51.5% to 73.6% for landline and from 28.5% to 38.2% for cellular telephones.

To improve precision, Kaplan-Meier survival analysis of monthly interview data collected during September 2010--March 2011 was used to determine the cumulative proportion of persons vaccinated with ≥1 dose during August 2010--February 2011. BRFSS data were used to estimate coverage for adults aged ≥18 years (n = 199,452) and NIS data were used to estimate coverage for children aged 6 months--17 years (n = 88,580). Coverage for all persons aged ≥6 months was determined using combined child and adult state-level estimates weighted by the age-specific populations of each state.§ CDC performed Pearson correlations among children and among adults to determine whether state-specific coverage during 2010--11 was associated with coverage during the 2009--10 season. CDC also performed a Pearson correlation between 2010--11 child and adult estimates to determine whether coverage was associated between the two age groups. For children, estimated national seasonal coverage for 2010--11 was compared with 2009--10 national seasonal coverage (4,5). For adults and persons aged ≥6 months, to make valid comparisons across years, coverage for 2009--10 was restricted to the 43 states and DC with available data in 2010--11. Student t tests were used to determine statistical significance in differences between groups and between the 2009--10 and 2010--11 vaccination seasons.

Coverage by Age Group

Among children aged 6 months--17 years, estimated national coverage was 49.0%, 6.7 percentage points higher than 2009--10 national seasonal coverage (42.3%) (Table 1) (4). State-specific coverage for children ranged from 33.2% (Montana) to 85.4% (Hawaii). Coverage among the 43 states and DC for adults aged ≥18 years was 40.9%, similar to 2009--10 seasonal coverage (40.5%); state-specific coverage ranged from 31.6% (Alaska) to 50.5% (Iowa). State-specific child and adult coverage levels had a correlation of 0.39, and coverage levels among children were more variable than those among adults. State-specific coverage in 2010--11 was positively correlated with 2009--10 seasonal coverage for children (r = 0.79) and for adults (r = 0.79).

Among the 43 states and DC, coverage for adults aged 18--49 years for the 2010--11 season was 30.2%, similar to coverage for the 2009--10 season (30.3%); state-specific coverage ranged from 22.1% (Florida) to 43.6% (North Dakota). Coverage for adults aged 50--64 years was 45.6%, comparable to 2009--10 coverage (44.8%); state-specific coverage ranged from 33.2% (Alaska) to 54.2% (Minnesota). Coverage for adults aged ≥65 years was 68.6%, comparable to 2009--10 coverage (68.9%); state-specific coverage ranged from 54.0% (Alaska) to 79.5% (North Carolina). Coverage for adults aged 18--64 years with a medical condition that increased their risk for severe influenza was 48.4% and state-specific coverage ranged from 28.2% (Alaska) to 71.9% (North Dakota).¶

Coverage by Race/Ethnicity

Among all persons aged ≥6 months, coverage among the 43 states and DC was higher for non-Hispanic whites (44.0%) compared with non-Hispanic blacks (38.8%) and Hispanics (40.6%) and similar to coverage for non-Hispanic others (42.8%) (Table 2). Among adults, non-Hispanic whites (43.3%; 95% confidence interval [CI] = 42.7--43.9) had the highest coverage, followed by non-Hispanic others (39.0%; CI = 35.9--42.1), and non-Hispanic blacks (34.9%; CI = 32.5--37.3) and Hispanics (32.4%; CI = 29.7--35.1). Adult coverage for non-Hispanic whites, Hispanics, and non-Hispanic others in 2010--11 was comparable to 2009--10 seasonal levels (43.8%, 30.6%, 37.8%, respectively), but was 3.6 percentage points higher in 2010--11 for non-Hispanic blacks. Among children, national coverage was higher for Hispanics (55.3%; CI = 51.7--58.9) and non-Hispanic others (53.6%; CI = 49.6--57.6) compared with non-Hispanic whites (46.3%; CI = 45.0--47.6), and Hispanics also had higher coverage than non-Hispanic blacks (47.9%; CI = 43.3--52.5). Among children, 2010--11 coverage for non-Hispanic others was comparable to 2009--10 national seasonal levels (51.8%), but was 3.8, 11.4, and 12.4 percentage points higher for non-Hispanic whites (42.5%), Hispanics (43.9%), and non-Hispanic blacks (35.5%), respectively.

Coverage by Month

Of the two age groups with recent ACIP recommendations to receive annual influenza vaccination, coverage levels among children aged 6 months--17 years were higher for all months of the 2010--11 season compared with monthly estimates from the 2009--10 season (Figure). Adults aged 18--49 years had monthly vaccination coverage estimates that were comparable for all vaccination months of the 2009--10 season, except for September and October.

Reported by

Carolyn Furlow, PhD, Amparo G. Gonzalez-Feliciano, MPH, Leah N. Bryan, MS, Gary L. Euler, DrPH, Helen Ding, MD, James A. Singleton, MS, Immunization Svc Div; Lina S. Balluz, ScD, Div of Behavioral Science, Office of Surveillance, Epidemiology, and Laboratory Svcs, CDC. Corresponding contributor: Carolyn Furlow, [email protected], 404-639-8407.

Editorial Note

For the 2010--11 season, ACIP recommendations for annual vaccination for all persons aged ≥6 months went into effect, memories of the 2009 H1N1 pandemic were fresh in the public's mind, and approximately 48 million more seasonal vaccine doses were distributed than for the 2009--10 season. A moderate increase in child vaccination coverage was observed compared with coverage for the 2009--10 season, although the increase was not as large as that observed from 2008--09 to 2009--10 among 19 states (5). School-located H1N1 vaccination was used in many communities (6), and that strategy might have found greater use in some areas during the 2010--11 season. Higher coverage in children also might reflect the second full year since expansion of ACIP influenza vaccination recommendations to include all children aged 6 months--18 years, with increased offering by vaccination providers and acceptance by parents (7). Although 2010--11 was the first season the ACIP expanded recommendations to include all adults aged 19--49 years to receive annual influenza vaccination, no significant increase in coverage occurred, underscoring the challenges associated with increasing coverage in this group.

Influenza vaccination coverage between states varied widely, particularly for children and for adults aged 18--64 years with high-risk conditions. In addition, state-level seasonal coverage levels for 2010--11 correlated positively with levels achieved in 2009--10. Lessons learned from states with high vaccination coverage should be imparted to states with lower coverage.

The 2010--11 estimates of national coverage levels and monthly vaccination for children aged 6 months--17 years indicated that children began receiving their vaccinations slightly earlier in the season and received more vaccine overall compared with 2009--10 seasonal levels; for adults aged 18--49 years, coverage levels and monthly vaccination closely mirrored those from 2009--10. During the vaccination period, coverage among children increased more rapidly compared with adults aged 18--49 years. National Influenza Vaccination Week, December 5--11, 2010 (8), was established to highlight the importance of continuing vaccination through December and beyond; its campaign efforts might have contributed to increased coverage levels into December and January, as observed for children in particular.

The pattern of lower influenza vaccination coverage for Hispanics and non-Hispanic blacks compared with non-Hispanic whites among persons aged ≥6 months also has been observed in previous seasons overall (5) and among adults (9). Although racial/ethnic disparities in vaccination coverage among adults persisted, the gap in coverage decreased somewhat. Improved coverage among non-Hispanic black and Hispanic children eliminated racial/ethnic disparities in child coverage during the 2010--11 season. This increase in coverage might be attributed partly to the Vaccines for Children program, which provides vaccines at no cost to children from low-income homes.**

The findings in this report are subject to at least six limitations. First, influenza vaccination status was based on self or parental report, was not validated with medical records, and thus is subject to recall bias. Second, BRFSS and NIS are telephone-based surveys that do not include households without telephone service, and BRFSS data analyzed do not include households with cellular telephone service only. Third, response rates for both surveys were low, and nonresponse bias might remain, even after weighting adjustments to reflect the national population subgroup distribution and nonresponse. Fourth, combining BRFSS and NIS estimates allowed estimation of coverage for all persons aged ≥6 months; however, differences in survey methodology (e.g., different sampling frame, survey design, exact survey question wording, response rates, and weighting) might result in different levels of bias that are averaged for this group. Fifth, BRFSS adult interview data through March were not available for seven states, thus creating potential bias in comparisons between child and adult estimates. Only small differences (range: 0.0--2.9 percentage points) were observed, however, when comparisons between 2009--10 coverage among the 43 states and DC were made with 2009--10 national coverage by age and race/ethnicity group. This suggests that coverage for the seven missing states together did not differ substantially from the nation. Finally, vaccination coverage comparisons of the trivalent formulations between 2010--11 and 2009--10 do not account for persons who received only H1N1 vaccination during 2009--10.

Record high vaccination coverage was sustained during 2010--11, a nonpandemic year, with increases in national coverage observed for children compared with 2009--10 seasonal coverage. Racial/ethnic disparities were not observed among children because of large gains in coverage for non-Hispanic black and Hispanic children compared with 2009--10 levels. In spite of these gains, further work remains to reduce racial/ethnic disparities among adults and to bring annual seasonal vaccination coverage levels up to Healthy People 2020 targets of 80% for persons aged 6 months--64 years, and 90% for adults aged 18--64 years with high-risk conditions and adults aged ≥65 years (10). With universal vaccination recommendations and consistent vaccine availability, substantial opportunities remain to increase coverage further. Expanded access through greater use of pharmacy, workplace, and school venues for vaccination, and better use of evidence-based practices at medical sites (e.g., standing orders, and reminder/recall notification) are important to building on these gains in vaccination coverage.

Acknowledgments

Kennon R. Copeland, PhD, Margrethe Montgomery, MA, Nicholas Davis, MS, Lin Liu, MS, National Opinion Research Center, Chicago, Illinois. State BRFSS coordinators.

References

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