Table 1. Characteristics of patients ≥ 60 years old admitted to hospital and included in the influenza vaccine effectiveness study, Valencia Hospital Network for the Study of Influenza (VAHNSI), Spain, 2017/18 influenza season (n = 1,477 patients).

Characteristics	Influenza positive		Influenza negative		p valuec	Number vaccinated in 2017/18	Total	%d	p value
	n	%a	n	%b
Overall (n  =  1,477)	483	32.7	994	67.3	NA	759	1,477	51.4	NA
Age in years
60–69	88	18.2	203	20.4	0.218	99	291	34.0	< 0.001
70–79	166	34.4	289	29.1		244	455	53.6
80–89	177	36.6	384	38.6		327	561	58.3
≥ 90	52	10.8	118	11.9		89	170	52.4
Sex
Male	234	48.4	526	52.9	0.107	420	760	55.3	0.002
Female	249	51.6	468	47.1		339	717	47.3
Underlying conditions (number)
None	29	6.0	76	7.6	0.181	35	105	33.3	< 0.001
One	122	25.3	214	21.5		154	336	45.8
Two or more	332	68.7	704	70.8		570	1,036	55.0
Admission in the last 12  months
Yes	140	29.0	346	34.8	0.025	485	991	48.9	0.007
No	343	71.0	648	65.2		274	486	56.4
GP visits in the last 3  months
None	145	30.0	314	31.6	0.814	223	459	48.6	0.126
One	56	11.6	116	11.7		82	172	47.7
Two or more	282	58.4	564	56.7		454	846	53.7
Smoking habits
Never	256	53.0	427	43.0	< 0.001	350	683	51.2	< 0.001
Ex-smoker	158	32.7	425	42.8		336	583	57.6
Current smoker	69	14.3	142	14.3		73	211	34.6
Socioeconomic statuse
Professional	57	11.8	119	12.0	0.953	88	176	50.0	0.527
Skilled	43	8.9	93	9.4		76	136	55.9
Unskilled	383	79.3	782	78.7		595	1,165	51.1
Obesity f
No	356	73.7	733	73.7	0.988	556	1,089	51.1	0.669
Yes	127	26.3	261	26.3		203	388	52.3
Days from onset to swab
0–2	74	15.3	175	17.6	0.310	131	249	52.6	0.153
3–4	212	43.9	387	38.9		300	599	50.1
5–7	157	32.5	348	35.0		274	505	54.3
> 7	40	8.3	84	8.5		54	124	43.5
Current and prior vaccination
Vaccinated 2017/18	242	50.1	517	52.0	0.491	NA	NA	NA	NA
Vaccinated 2016/17	241	49.9	528	53.1	0.245	663	769	86.2	< 0.001
Vaccinated 2015/16	254	52.6	544	54.7	0.439	651	798	81.6	< 0.001
Influenza test resultsg
Negative	0	0.0	994	100.0	NA	517	994	52.0	0.491
A(H1N1)pdm09	81	16.8	0	0.0	NA	30	81	37.0	0.008
A(H3N2)	232	48.0	0	0.0	NA	132	232	56.9	0.067
B/Yamagata lineage	150	31.1	0	0.0	NA	69	150	46.0	0.405
B/Victoria lineage	1	0.2	0	0.0	NA	1	1	0.0	0.272

GP: general practitioner.

^a Except for the ‘Overall’ category line of the Table, where the percentages are calculated relative to the total number of patients included in the analysis (i.e. 1,477), the rest of the percentages presented in this column are based on the total of patients testing positive for influenza (i.e. 483).

^b Except for the ‘Overall’ category line of the Table, where the percentages are calculated relative to the total number of patients included in the analysis (i.e. 1,477), the rest of the percentages presented in this column are based on the total of patients testing negative for influenza (i.e. 994).

^c These p values identify whether there is a dependence between the laboratory-confirmed influenza variable and the characteristics on the left, e.g. age. P values < 0.05 indicate that influenza cases and influenza controls were not equally distributed according to the explored characteristics on the left.

^d Percentages in this column are based on the numbers and totals displayed in the two previous columns.

^e Socioeconomic status: ‘professional’ includes professionals, managers, medium or superior technicians, small entrepreneurs, middle managers, supervisors; ‘skilled’ includes skilled manual workers; ‘unskilled’ includes semi-skilled and unskilled manual workers.

^f Obesity was defined as a body mass index (BMI) ≥ 30.

^g Fifteen influenza A and four influenza B samples were not subtyped because of low viral loads.

Bold font is used to highlight p values indicating statistical significance.