Table 1. Sample characteristics of participants ≥18 years in the United States, by age, high-risk status, and healthcare personnel -National Health Interview Survey, the 2004-05 through 2010-2011 seasons.

	2004-05 Seasonaa		2005-06 Seasonb		2006-07 Seasonb		2007-08 Seasonb		2008-09 Seasonb		2009-10 Seasonb		2010-11 Seasonb
	Sample size	Weighted %	Sample size	Weighted %	Sample size	Weighted %	Sample size	Weighted %	Sample size	Weighted %	Sample size	Weighted %	Sample size	Weighted %
Age group
≥18 years	14,958	100.0	22,959	100.0	20,195	100.0	19,341	100.0	14,798	100.0	25,661	100.0	25,758	100.0
18-64 years	12,078	83.9	18,570	83.9	16,207	83.8	15,436	83.5	11,826	83.1	20,441	83.0	20,426	82.9
18-49 years	8,543	60.9	13,204	60.7	11,504	60.3	10,790	59.0	8,227	58.3	14,028	58.0	14,181	57.8
50-64 years	3,535	23.0	5,366	23.2	4,703	23.5	4,646	24.5	3,599	24.8	6,413	25.0	6,245	25.2
≥65 years	2,907	16.1	4,389	16.1	3,988	16.2	3,905	16.5	2,972	16.9	5,220	17.0	5,332	17.1
Persons with high-risk conditionsc
18-64 years	2,397	100.0	3,548	100.0	2,995	100.0	2,919	100.0	2,410	100.0	4,194	100.0	4,017	100.0
18-49 years	1,231	54.1	1,859	53.8	1,543	52.8	1,488	53.5	1,213	51.6	2,039	50.6	1,961	50.0
50-64 years	1,166	45.9	1,689	46.2	1,452	47.2	1,431	46.5	1,197	48.4	2,155	49.4	2,056	50.0
Persons without high-risk conditions
18-64 years	9,660	100.0	14,979	100.0	13,177	100.0	12,479	100.0	8,769	100.0	16,208	100.0	15,570	100.0
18-49 years	7,296	76.9	11,313	76.5	9,943	76.1	9,281	74.6	6,374	72.1	11,962	74.7	11,544	74.2
50-64 years	2,364	23.1	3,666	23.5	3,234	23.9	3,198	25.4	2,395	27.9	4,246	25.3	4,026	25.8
Health-care personneld ≥18 years	1,020	6.8e	1,638	6.9e	1,484	7.2e	1,490	7.6e	1,185	7.6e	1,860	7.8e	2,112	8.2e

^aThis is based on interviews conducted during January through June 2005.

^bThis is based on interviews conducted during September through June for each influenza season (e.g., the 2005-06 season included persons interviewed during September 2005 through June 2006).

^cAdults categorized as being at high risk for influenza-related complications self-reported one or more of the following: 1) ever being told by a physician they had diabetes, emphysema, coronary heart disease, angina, heart attack, or other heart condition; 2) having a diagnosis of cancer during the preceding 12 months (excluding non-melanoma skin cancer) or ever being told by a physician they have lymphoma, leukemia, or blood cancer during the previous 12 months; 3) being told by a physician they have chronic bronchitis or weak or failing kidneys; or 4) reporting an asthma episode or attack during the preceding 12 months.

^dDuring the 2005-06 through 2008-09 seasons, adults were classified as health-care personnel if they were ≥18 years and currently employed in a health-care occupation or in a health-care--industry setting, on the basis of standard occupation and industry categories recoded in groups by National Center for Health Statistics, Centers for Disease Control & Prevention. From the 2009-10 to 2010-11 seasons, health-care personnel is defined as adults ≥18 years who currently volunteer or work in a hospital, medical clinic, doctor's office, dentist's office, nursing home or some other health-care facility including part-time and unpaid work in a health care facility as well as professional nursing care provided in the home.

^eThis number indicates the percentage of adults ≥18 years who are health-care personnel.