Table 2. Health characteristics of individuals included in the study (an individual may have been involved in 1, 2, or 3 seasons).

	2012–2013, n (%)	2013–2014, n (%)	2014–2015, n (%)
N	1756	1424	1726
Colds/flu-like diseases frequency (MD = 69)
Rare	1291 (74.5)	1011 (72.1)	1285 (75.5)
Often	421 (24.3)	363 (25.9)	393 (23.1)
Don’t know	20 (1.2)	28 (2.0)	25 (1.4)
Flu vaccination for the current season (MD = 0)
No	1360 (77.5)	1062 (74.5)	1278 (74.0)
Yes	394 (22.4)	361 (25.4)	445 (25.8)
Don’t know	2 (0.1)	1 (0.1)	3 (0.2)
Smoking status (MD = 0)
Never smoked	1019 (58.0)	819 (57.5)	997 (57.8)
Used to smoke	480 (27.4)	408 (28.7)	517 (30.0)
Still smoking	257 (14.6)	197 (13.8)	212 (12.2)
Comorbidities (MD = 0)
No comorbidities	1430 (81.4)	1135 (79.7)	1363 (79.0)
≥1 comorbidity	326 (18.6)	289 (20.3)	363 (21.0)
Treated asthma	131 (7.5)	118 (8.3)	144 (8.3)
Treated diabetes	48 (2.7)	47 (3.3)	48 (2.8)
Treated heart condition	119 (6.8)	90 (6.3)	142 (8.2)
Treated kidney condition	7 (0.4)	10 (0.7)	9 (0.5)
Treated immunodepression	47 (2.7)	40 (2.8)	49 (2.8)
Treated pulmonary condition	50 (2.8)	51 (3.6)	58 (3.4)
≥1 respiratory allergy (MD = 0)	677 (38.6)	566 (39.7)	659 (38.2)
Pregnancy (MD = 35)
Pregnant	7 (0.4)	8 (0.6)	24 (1.4)
Not pregnant	544 (31.3)	424 (29.9)	512 (29.8)
Not applicable (men or women <15 or >50 years old)	1188 (68.3)	984 (69.5)	1180 (68.8)
BMI, kg/m2 (MD = 73)
<18.5	200 (11.6)	156 (11.1)	190 (11.2)
18.5–29	1348 (78.1)	1081 (76.8)	1296 (76.2)
30–39	158 (9.2)	152 (10.8)	197 (11.5)
≥40	19 (1.1)	19 (1.3)	18 (1.1)
At risk of influenza complications (MD = 85)
No	1215 (70.8)	954 (67.8)	1114 (65.6)
Yes	501 (29.2)	453 (32.2)	584 (34.4)

BMI = body mass index. MD = missing data.