Table 4. Effect of seasonal influenza vaccination in reducing severity among subgroups of patients hospitalised due to laboratory-confirmed influenza, Catalonia, Spain, influenza seasons 2010/11–2015/16 (n = 1727).

Analysis subset	ICU/death	Non-ICU/death	Crude vaccination effect	95% CI	Adjusted vaccination effect (%)	95% CI	p-value
Sex
Female	271	472	27	-5 to 49	3	-43 to 34	0.886
Male	421	563	43	22 to 57	33	8 to 51	0.014
Age
18–64	386	422	6	-53 to 43	13	-42 to 47	0.574
≥ 65	306	613	33	-2 to 42	25	-1 to 43	0.050
NI treatment
Yes	635	942	36	18 to 49	21	-2 to 39	0.070
No	57	93	37	-30 to 70	57	2 to 81	0.031

CI: confidence interval; ICU: intensive care unit; NI: Neuraminidase inhibitors.