Final state-level influenza vaccination coverage estimates for the 2010–11 season–United States, National Immunization Survey and Behavioral Risk Factor Surveillance System, August 2010 through May 2011

Key Findings

• Influenza vaccination coverage among children increased for the 2010–11 season compared to 2009–10 seasonal (trivalent) coverage. Over the past two seasons, coverage was stable for adults ≥18 years.

Coverage by age groups

• Among persons ≥6 months, the estimated national influenza vaccination cumulative coverage through May was 43.0% (Table 1), 1.8 percentage-points higher than 2009–10 seasonal (trivalent) coverage (3). State-specific coverage ranged from 55.6% (South Dakota) to 36.5% (Florida) (1).
• Among children 6 months–17 years, the estimated national coverage (≥1 or more doses for children <9 years) was 51.0%, 7.3 percentage-points higher than 2009–10 seasonal (trivalent) coverage. State-specific coverage for children 6 months–17 years ranged from 79.3% (Rhode Island) to 37.3% (Montana).
• Among adults ≥18 years, the estimated national coverage was 40.5%, comparable to 2009–10 seasonal (trivalent) coverage (40.4%). State-specific coverage for adults ≥18 years ranged from 56.2% (South Dakota) to 32.7% (Nevada).
• Among all age groups, the estimated national coverage varied widely. Coverage for children decreased with increasing age; 68.2% of children 6–23 months received 1 or more doses of influenza vaccine, compared to 60.6% among children 2–4 years, 54.7% among children 5–12 years and 34.5% among children 13–17 years. In contrast, the coverage for adults increased with increasing age. For adults 18–49 years coverage was 30.5%, for adults 50–64 years coverage was 44.5%, and for adults ≥65 years coverage was 66.6%.
• Among adults 18–49 years, the estimated national coverage for the 2010–11 season was similar to 2009–10 seasonal (trivalent) coverage (29.9%, 95% Confidence Interval [CI] 29.4–30.4, for 2009–10 season) (CDC unpublished), and was 2.3 percentage-points higher than 2008–09 coverage (28.2%, CI 27.4–29.0).
• Among adults 50–64 years, the estimated national coverage for the 2010–11 season was similar to 2009–10 seasonal (trivalent) coverage (45.0%, CI 44.4–45.6), and was 1.4 percentage-points lower than 2008–09 coverage (45.9%, CI 45.1–46.7).
• Among adults ≥65 years, the estimated national coverage for the 2010–11 season was 3.0 percentage-points lower than 2009–10 seasonal (trivalent) coverage (69.6%, CI 69.0–70.2), and was 7.0 percentage-points lower than 2008–09 coverage (73.6%, CI 73.0–74.2).
• Among adults 18–64 years with at least one selected high-risk condition measured by BRFSS (asthma, diabetes or heart disease), estimated national coverage was 46.7%, similar to 2009–10 seasonal (trivalent) coverage (46.2%, CI 45.2–47.2) and 2008–09 coverage (47.9%, CI 46.5–49.3). State-specific coverage varied widely, ranging from 68.4% (South Dakota) to 33.7% (Alaska).

Coverage by sex

• Among adults 18–64 years, the estimated national coverage was 6.0 percentage-points higher for females compared with males, 37.8% and 31.8% respectively (Table 1). Among high-risk adults 18–64 years, coverage was 6.1 percentage-points higher for females compared to males, 49.4% and 43.3% respectively. For child age groups and adults ≥65 years, the coverage between sexes was comparable.

Coverage by race/ethnicity

• Among persons ≥6 months, coverage among non-Hispanic whites (44.3%) was higher than that of non-Hispanic blacks (39.0%) and Hispanics (40.0%), and was similar to coverage among Asians (43.1%), American Indians and Alaska Natives (AIAN) (42.1%), and non-Hispanic others (42.9%) (Table 2).
• Among children 6 months–17 years, coverage among non-Hispanic blacks (50.8%) was comparable to non-Hispanic whites (48.5%). Coverage was higher for Asians (59.4%), Non-Hispanic others (55.6%), and Hispanics (55.1%) compared to non-Hispanic whites (48.5%). The 2010–11 coverage was 5.3, 8.2, and 13.8 percentage-points higher than 2009–10 seasonal (trivalent) coverage for non-Hispanic whites (43.2%), Hispanics (46.9%), and non-Hispanic blacks (37.0%), respectively.
• Among adults ≥18 years, non-Hispanic whites had the highest coverage (43.2%) compared to Hispanics (32.3%), non-Hispanic blacks (34.2%), non-Hispanic others (37.4%), and Asians (38.2%). Adult coverage for non-Hispanic whites, non-Hispanics blacks, and non-Hispanic others (Total) in 2010–11 was comparable to 2009–10 seasonal (trivalent) coverage (44.1%, 32.8%, 38.7%, respectively), but was 3.0 percentage-points higher in 2010–11 for Hispanics (29.3%).

Coverage by Month

• Among persons ≥6 months, 2010–11 coverage was higher for all months except September and October compared to 2009–10 monthly seasonal (trivalent) influenza vaccination coverage (Figure 1).
• Among children 6 months–17 years, monthly coverage was higher for 2010–11 season compared to 2009–10 monthly seasonal (trivalent) coverage (Figure 2).
• Among adults ≥18 years, 2010–11 monthly coverage estimates were comparable to the 2009–10 monthly seasonal (trivalent) coverage (Figure 3).

Estimated Numbers of Persons Vaccinated

• Among persons ≥6 months, the estimated number of those receiving one or more seasonal influenza vaccine doses were 36.6 million (CI 36.0–37.3 million) children (6 months–17 years) and 94.2 million (CI 93.3–95.1 million) adults (≥18 years), for an estimated 130.9 million (CI 129.7–132.1 million) seasonal influenza vaccinees during August 2010 through May 2011.

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Table 1: Estimated influenza vaccination coverage^*by age groups and by sex – Behavioral Risk Factor Surveillance System (BRFSS) and National Immunization Survey (NIS), United States, ^† end of May 2011

	Total			Male			Female
Age groups	Unweighted sample size	%‡	95% CI§	Unweighted sample size	%	95% CI	Unweighted sample size	%	95% CI
All persons
≥6 mos	494,368	43.0	(±0.4))	202,213	40.6	(±0.7)	292,155	45.2	(±0.5)
Children
6 mos–17 yrs	116,799	51.0	(±0.9)	60,272	50.8	(±1.3)	56,527	51.2	(±1.3)
6 mos–4 yrs	37,895	63.6	(±1.7)	19,441	63.6	(±2.4)	18,454	63.6	(±2.4)
6–23 mos	14,508	68.2	(±2.4)	7,433	67.7	(±3.3)	7,075	68.6	(±3.4)
2–4 yrs	23,387	60.6	(±2.3)	12,008	60.9	(±3.2)	11,379	60.4	(±3.2)
5–12 yrs	46,058	54.7	(±1.5)	23,738	54.1	(±2.1)	22,320	55.4	(±2.2)
13–17 yrs	32,846	34.5	(±1.4)	17,093	34.7	(±2.0)	15,753	34.2	(±1.9)
Adults
18+ yrs	377,569	40.5	(±0.4)	141,941	37.4	(±0.8)	235,628	43.3	(±0.6)
18-64 yrs	244,933	34.8	(±0.6)	95,051	31.8	(±0.8)	149,882	37.8	(±0.6)
18-64 yrs HR ||	41,826	46.7	(±1.4)	15,522	43.3	(±2.4)	26,304	49.4	(±1.8)
18-49 yrs	116,113	30.5	(±0.6)	44,716	27.5	(±1.0)	71,397	33.6	(±0.8)
18-49 yrs HR	14,711	39.0	(±2.2)	4,676	33.8	(±3.5)	10,035	42.6	(±2.5)
50-64 yrs	128,820	44.5	(±0.6)	50,335	41.9	(±1.0)	78,485	46.9	(±0.8)
65+ yrs	132,636	66.6	(±0.6)	46,890	66.5	(±1.0)	85,746	66.7	(±0.8)
* Weighted coverage estimates are for persons interviewed September 2010 through June 2011 who reported being vaccinated August 2010 through May 2011. † Excludes U.S. territories ‡ Month of vaccination was imputed for respondents with missing month of vaccination data. Percentages are weighted to the non–institutionalized, U.S. civilian population § Confidence interval || Selected high–risk conditions. Includes people with asthma, diabetes or heart disease.

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Table 2: Estimated influenza vaccination coverage^* by age groups and race/ethnicity–Behavioral Risk Factor Surveillance System (BRFSS) and National Immunization Survey (NIS), United States, ^† end of May 2011

	Non-Hispanic white			Non-Hispanic black			Hispanic
Age groups	Unweighted sample size	%‡	95% CI§	Unweighted sample size	%	95% CI	Unweighted sample size	%	95% CI
All persons
≥6 mos	377,124	44.3	(±0.4)	41,198	39.0	(±1.5)	40,119	40.0	(±1.4)
Children
6 mos–17 yrs	75,113	48.5	(±1.0)	12,182	50.8	(±2.9)	17,598	55.1	(±2.6)
6 mos–4 yrs	23,422	62.9	(±2.0)	3,923	59.1	(±6.1)	6,213	66.2	(±3.7)
6–23 mos	8,934	68.2	(±2.9)	1,542	65.1	(±8.2)	2,338	67.9	(±5.2)
2–4 yrs	14,488	59.6	(±2.5)	2,381	55.6	(±8.3)	3,875	65.0	(±5.0)
5–12 yrs	30,314	51.5	(±1.6)	4,563	54.6	(±4.5)	6,447	60.5	(±4.2)
13–17 yrs	21,377	32.9	(±1.4)	3,696	38.4	(±5.0)	4,938	34.6	(±3.7)
Adults
≥18 yrs	302,011	43.2	(±0.4)	29,016	34.2	(±1.8)	22,521	32.3	(±1.6)
18-64 yrs	188,853	36.6	(±0.6)	21,059	30.9	(±1.8)	18,016	29.7	(±1.6)
18-64 yrs HR ||	30,818	48.1	(±1.6)	4,566	42.6	(±4.9)	2,984	44.6	(±5.3)
18-49 yrs	84,099	31.6	(±0.8)	10,743	28.1	(±2.4)	11,929	27.1	(±2.0)
18-49 yrs HR	10,209	39.2	(±2.4)	1,712	37.1	(±6.9)	1,415	37.3	(±6.5)
50-64 yrs	104,754	45.7	(±0.8)	10,316	38.4	(±2.4)	6,087	41.9	(±3.3)
≥65 yrs	113,158	67.7	(±0.6)	7,957	56.1	(±3.3)	4,505	66.8	(±3.7)

Table 2 continued.

Non-Hispanic Other
	Non-Hispanic Other (Total)			Asian			AIAN			Other**
Age groups	Unweighted sample size	%‡	95% CI§	Unweighted sample size	%	95% CI	Unweighted sample size	%	95% CI	Unweighted sample size	%	95% CI
All persons
≥6 mos	31,453	42.9	(±1.6)	10,083	43.1	(±2.8)	6,731	42.1	(±4.0)	14,639	42.9	(±2.5)
Children
6 mos–17 yrs	11,906	57.1	(±2.9)	4,113	59.4	(±4.7)	1,786	55.7	(±8.0)	6,007	55.6	(±4.1)
6 mos–4 yrs	4,337	67.8	(±5.1)	1,414	70.2	(±8.5)	625	62.3	(±11.5)¶	2,298	67.0	(±7.3)
6–23 mos	1,694	74.0	(±6.5)	534	75.3	(±10.4)¶	253	71.7	(±15.3)¶	907	73.7	(±9.3)
2–4 yrs	2,643	63.6	(±7.2)	880	71.2	(±13.3)¶	372	56.3	(±16.1)¶	1,391	61.3	(±9.3)
5–12 yrs	4,734	60.2	(±4.4)	1,729	61.7	(±6.7)	743	62.4	(±13.1)¶	2,262	58.8	(±6.5)
13–17 yrs	2,835	39.3	(±4.9)	970	41.9	(±8.9)	418	33.7	(±9.2)	1,447	38.7	(±6.7)
Adults
≥18 yrs	19,547	38.0	(±2.0)	5,970	38.2	(±3.3)	4,945	39.0	(±4.5)	8,632	37.4	(±3.1)
18-64 yrs	14,630	35.2	(±2.2)	4,624	36.1	(±3.5)	3,822	34.9	(±4.9)	6,184	34.3	(±3.3)
18-64 yrs HR ||	2,972	44.8	(±5.1)	484	42.8	(±10.4)¶	950	41.3	(±10.2)¶	1,538	47.3	(±7.1)
18-49 yrs	8,339	32.6	(±2.7)	2,982	33.4	(±3.9)	2,108	31.3	(±6.1)	3,249	32.1	(±4.3)
18-49 yrs HR	1,238	41.6	(±7.1)	217	34.0	(±12.5)¶	382	40.3	(±14.5)¶	639	45.5	(±9.8)
50-64 yrs	6,291	44.2	(±3.1)	1,642	49.3	(±5.7)	1,714	44.6	(±6.7)	2,935	40.5	(±4.3)
≥65 yrs	4,917	64.5	(±3.3)	1,346	67.9	(±6.3)	1,123	68.7	(±8.0)	2,448	60.7	(±4.3)
* Weighted coverage estimates are for persons interviewed September 2010 through June 2011 who reported being vaccinated August 2010 through May 2011. † Excludes U.S. territories ‡Month of vaccination was imputed for respondents with missing month of vaccination data. Percentages are weighted to the non-institutionalized, U.S. civilian population || Selected high-risk conditions. Includes people with asthma, diabetes or heart disease. ¶ Estimates might be unreliable because confidence interval half-width is >10. ** Includes Native Hawaiian or other Pacific Islander, multiracial, and other races.

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Figure 1: Coverage Estimates by Influenza Season, United States―Persons ≥6 months

Figure 2: Coverage Estimates by Influenza Season, United States―Children 6 months–17 years

Figure 3: Coverage Estimates by Influenza Season, Unites States―Adults ≥18 years

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Summary and Public Health Implications

Findings of this report are consistent with the previous published estimates (2). A moderate increase in child vaccination coverage was observed for each month of the 2010–11 season compared to 2009–10 seasonal (trivalent) coverage, whereas the monthly vaccination coverage levels among adults closely mirrored the 2009–10 seasonal (trivalent) coverage levels. This is the first season under the Advisory Committee on Immunization Practices (ACIP) recommendation for annual influenza vaccination for all persons ≥6 months and the second season under the ACIP recommendation for annual influenza vaccination for children 6 month–18 years (4).

During the 2010–11 season, influenza vaccination coverage between states varied widely, particularly for children and for adults aged 18–64 years with high-risk conditions. Possible reasons that may explain part of the variation by state could include differences in medical-care delivery infrastructure, population norms, and effectiveness of state and local immunization programs. The presence of advocates for influenza vaccination efforts using techniques such as school-located vaccination (5), drive through vaccination campaigns (6), and text messaging promotions (7) may positively affect local vaccination coverage.

Similar to what was observed for 2009–10 seasonal (trivalent) vaccination, Hispanic and non-Hispanic black adults had lower vaccination coverage than non-Hispanic white adults. However, no disparities were observed for Hispanic and non-Hispanic black children compared to non-Hispanic white children in 2010–11. This is in contrast to the disparities observed for seasonal (trivalent) influenza vaccination coverage in the 2009–10 season. Coverage among children increased for each of these racial/ethnic groups from 2009–10 to 2010–11 seasons, but the increases were larger for Hispanic and non-Hispanic blacks, resulting in lack of racial/ethnic disparities in child coverage for the 2010–11 season.

Overall, influenza vaccination coverage among children increased for the 2010–11 season compared to 2009–10 seasonal (trivalent) coverage, remained stable for adults 18–64 years, and decreased for adults ≥65 years. The 2009–10 season was unique for several reasons, such as the heightened awareness about influenza due to the 2009 H1N1 pandemic, and recommendation for two influenza vaccinations, the seasonal (trivalent) vaccine and the pandemic 2009 H1N1 (monovalent) vaccine (8). These unique circumstances likely affected uptake of influenza vaccination during the 2009–10 season, and may have influenced influenza vaccination behavior in 2010–11. For children, comparable BRFSS data from all states for the 2008–09 season were not collected. Estimates of influenza vaccination among children for the 2008–09 season were 24% from 19 states from BRFSS (9) and 29% from the National Health Interview Survey (10). Although the estimates from these two earlier surveys may not be directly comparable to the estimates in this report, these 2008–09 estimates are substantially lower than the 2009–10 seasonal (trivalent) coverage and 2010–11 child coverage estimates. The increases in child coverage may be related to implementation of the ACIP recommendations in this age group, and heightened awareness of risks of influenza associated with the 2009–10 pandemic (e.g., children were included in the initial target group for 2009 H1N1 vaccination). Among adults 18–49 years, influenza vaccination coverage increased from the 2008–09 to 2010–11 season by two percentage-points, which may reflect the first year under the ACIP recommendation for vaccination of all persons ≥6 months and effects of the pandemic season. Among adults ≥65 years, coverage dropped by four percentage-points from 2008–09 to 2009–10 seasonal (trivalent) coverage and by three percentage-points from 2009–10 to 2010–11. The decline in coverage for adults ≥65 years may be at least partially related the ACIP recommendation that 2009 H1N1 vaccination of this age group be considered only after demand for vaccination among the initial target groups had been met (11).

For all groups, influenza vaccination coverage for the 2010–11 season remained well below the Healthy People 2020 targets of 80% for persons 6 months–64 years and 90% for adults ≥65 years and adults 18–64 years with high-risk conditions. Racial/ethnic disparities in influenza vaccination among adults remained, coverage among adults ≥65 years appears to have declined the past two seasons, and considerable variation in coverage by state was observed. Substantial opportunities remain to increase coverage, such as expanding 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, reminder/recall notification) (2, 12). Continued efforts are needed to ensure those at highest risk of influenza complications (i.e. elderly, young children, pregnant women, and persons with chronic health conditions) are vaccinated each year.

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Data Source and Methods

CDC analyzed data collected September 2010 through June 2011 from the NIS and the BRFSS from all 50 states and the District of Columbia to estimate national and state level influenza vaccination coverage for the 2010–11 influenza vaccination season. For comparison, 2008-09 coverage levels were estimated for adults using 2008-09 BRFSS data from all states, and for children from previously published estimates from the National Health Interview Survey (10) and from BRFSS in 19 states (9).

NIS is an ongoing, national landline list-assisted random-digit-dialed telephone survey of households with children who are 19–35 months or 13–17 years (NIS-Teen) at the time of interview. For children 6–18 months and 3–12 years identified during screening households for NIS and NIS-Teen, a short influenza vaccination module was added. A supplemental cellular phone sample was conducted as part of the NIS during 4th quarter 2010 and all quarters of 2011. NIS respondents ≥18 years were asked if their children had received a ‘flu’ vaccination since August 2010, and if so, in which month and year. The NIS Council of American Survey and Research Organizations (CASRO)* response rates across three quarters of data collection ranged from 38.1%–73.6% for landline and 26.4%–35.8% for cellular telephones. BRFSS is an on-going state-based monthly telephone survey which collects information on health conditions and risk behaviors from ~400,000 randomly selected persons ≥18 years among the non-institutionalized, U.S. civilian population. BRFSS respondents were asked if they had received a ‘flu’ vaccine in the past 12 months, and if so, in which month and year. The median state CASRO BRFSS response rate was 54.4%.

Kaplan-Meier survival analysis was used to determine the cumulative influenza vaccination coverage (≥1 dose) during August 2010 through May 2011 using monthly interview data collected September 2010 through June 2011. NIS data (n=116,799) were used to estimate coverage for children 6 months–17 years and BRFSS data (n=377,569) were used to estimate coverage for adults ≥18 years. Coverage estimates for all persons ≥6 months was determined using combined state-level monthly estimates weighted by the age-specific populations of each state. For participants who indicated they had been vaccinated but had a missing month and year of vaccination, this information was imputed from donor pools matched for week of interview, age group, state of residence and race/ethnicity. Results from both surveys were weighted and analyzed with SAS and SUDAAN statistical software to account for the complex survey design. Student t tests were used to determine statistical significance in differences between groups and between 2009–10 and 2010–11 vaccination coverage levels.

These estimates are subject to the following limitations. First, influenza vaccination status was based on self or parental report, was not validated with medical records, and thus is subject to respondent recall bias. Second, NIS and BRFSS are telephone-based surveys that do not include households without telephone service, and BRFSS data analyzed here do not include households with cellular telephone service only which may affect some geographic areas and racial/ethnic groups more than others (13). Third, response rates for both surveys were low and nonresponse bias may remain even after weighting adjustments. Fourth, combining NIS and BRFSS estimates allowed estimation of coverage for all persons ≥6 months; however, differences in survey methodology (e.g., different sampling frame, survey design, exact survey question wording, response rates and weighting) may result in different levels of bias that are averaged for this group. Fifth, the estimated number of persons vaccinated might be overestimated, as previous estimates resulted in higher numbers vaccinated than doses distributed (8). Finally, some age-by-state-specific estimates in the accompanying interactive reports (1) may be unreliable due to small sample size. The final estimates in these online reports are based on an additional three months or more of data collection compared to the interim results (2), and may differ from the interim estimates, particularly for estimates based on smaller sample sizes. Both final and interim estimates flagged as potentially unreliable should be interpreted with caution.

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References

1. CDC. Influenza vaccination coverage, 2010–11 influenza season. Available at http://www.cdc.gov/flu/professionals/vaccination/reporti1011/reportI/(https://www.cdc.gov/flu/professionals/vaccination/reporti1011/reporti/index.htm). Accessed September 20, 2011.
2. Interim results: state-specific seasonal influenza vaccination coverage – United States, August 2010-February 2011. MMWR 2011; 60(22):737-743.
3. CDC. Influenza vaccination coverage, 2009–10 influenza season. Available at http://www.cdc.gov/flu/professionals/vaccination/reporti0910/reportI0910/(https://www.cdc.gov/flu/professionals/vaccination/reporti0910/reporti0910/index.htm). Accessed September 7, 2011.
4. CDC. Prevention and control of influenza with vaccines: recommendations of the Advisory Committee on Immunization Practices (ACIP), 2010. MMWR 2010;59(No. RR-8).
5. Singleton, JA. Who got H1N1 vaccine? Findings from the U.S. 2009–2010 Influenza Vaccination Surveillance Systems. 44th National Immunization Conference. Atlanta, GA. Available at http://cdc.confex.com/cdc/nic2010/webprogram/Paper23190.html . Accessed June 3, 2011.
6. 45th National Immunization Conference. Record Breaking One Day Mass Drive-Through Flu Vaccine Program. Available at http://cdc.confex.com/cdc/nic2011/webprogram/Paper25318.html . Accessed September 9, 2011.
7. 45th National Immunization Conference. FluText: Using Text Messaging to Promote Timely Flu Vaccination In An Underserved Child Population. Available at http://cdc.confex.com/cdc/nic2011/webprogram/Paper25438.html . Accessed September 9, 2011.
8. CDC. Interim results: state-specific seasonal influenza vaccination coverage―United States, August 2009–January 2010. MMWR 2010;59:477–84.
9. CDC. Influenza vaccination coverage among children and adults – United States, 2008–09 influenza season. MMWR 2009;58:1091–1095.
10. CDC. 2009 Adult Vaccination Coverage, National Health Interview Survey (NHIS). Available at http://www.cdc.gov/vaccines/stats-surv/nhis/2009-nhis.htm. Accessed September 15, 2011.
11. CDC. Use of Influenza A (H1N1) 2009 Monovalent Vaccine: Recommendations of the Advisory Committee on Immunization Practices (ACIP), 2009. MMWR 2009;58(RR-10):1–8.
12. Guide to Community Preventive Services. Available at http://www.thecommunityguide.org/vaccines/universally/index.html . Accessed September 19, 2011.
13. Blumberg SJ Luke JV. Wireless substitution: Early release of estimates from the National Health Interview Survey, July-December 2010; 2011. Available at http://www.cdc.gov/nchs/data/nhis/earlyrelease/wireless201106.pdf[PDF – 310KB]. Accessed September 19, 2011.

* The CASRO response rate is the product of three other rates: 1) the resolution rate, which is the proportion of telephone numbers that can be identified as either for a business or residence; 2) the screening rate, which is the proportion of qualified households that complete the screening process; and 3) the cooperation rate, which is the proportion of contacted eligible households for which a completed interview is obtained.

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