Table 1.

Sample characteristics overall and per recruitment wave

		Wave 0		Wave 1		Wave 2		Waves 3–6		Total
		(n: 1105)		(n: 310)		(n: 93)		(n: 52)		(n: 1560)
		n	%	n	%	n	%	n	%	n	%
Country	Netherlands	1018	92.1	295	95.2	86	92.5	52	100	1451	93.0
	Belgium	87	7.9	15a	4.8	7	7.5	0	0	109	7.0
Sex	Male	387	35.0	122	39.4	31	33.3	10	19.2	550	35.3
	Female	718	65.0	188	60.6	62	66.7	42	80.8	1010	64.7
Ageb	0–39	139	12.5	91	29.3	26	28.0	13	25.0	268	17.2
	40–49	189	17.1	43	13.9	18	19.3	6	11.5	256	16.4
	50–64	496	44.9	106	34.2	32	34.4	22	42.3	656	42.1
	65+	281	25.5	70	22.6	17	18.3	11	21.2	379	24.3
Education	Bachelor or higher	651	58.9	166	53.5	56	60.2	23	44.2	896	57.4
	Lower than bachelor	144	41.1	29	46.5	37	39.8	29	55.8	664	42.6
Householdc	1-person	280	25.3	78	25.2	22	23.7	10	19.2	390	25.0
	2-persons	478	43.3	110	35.5	38	40.9	22	42.3	648	41.5
	3-persons	145	13.1	35	11.3	6	6.4	6	11.5	192	12.3
	4 or more persons	202	18.3	87	28.0	27	29.0	14	26.9	330	21.2
Work or Study	Yes	775	70.1	228	73.5	73	78.5	41	78.8	1117	71.6
	No	330	29.9	82	26.5	20	21.5	11	21.2	443	28.4
Vaccinatedd	Yes	516	46.7	104	33.5	19	20.4	15	28.8	654	41.9
	No	589	53.3	206	66.5	74	79.6	37	71.2	906	58.1
Symptoms	Yes	506	45.8	172	55.5	56	60.2	35	68.3	769	49.3
	No	599	54.2	138	44.5	37	39.8	17	32.7	791	50.7
Self-reported common cold	Yes	175	15.8	60	19.4	27	29.0	10	19.2	272	17.4
	No	930	84.2	250	80.6	66	71.0	42	80.8	1288	82.6
Self-reported influenza	Yes	96	8.7	24	7.7	7	7.5	3	5.8	130	8.3
	No	1009	91.3	286	92.3	86	92.5	49	94.2	1430	91.7
ILI	Yes	34	3.1	2	0.6	2	2.2	2	3.8	40	2.6
	No	1071	96.9	308	99.4	91	97.8	50	96.2	1520	97.4

^aOne participant lived in Germany

^bOne participant provided an invalid age

^cNote: 48 participants who completed the survey did not provide information on their household size and were assumed to live alone

^dVaccinated against influenza in the past 12 months