Table 2. Influenza vaccine effectiveness by vaccine type, regardless of vaccination history in patients ≥ 60 years old admitted to hospital, Valencia Hospital Network for the Study of Influenza (VAHNSI), Spain, 2017/18 influenza season (n = 1,477 patients).

Types, subtypes or lineage of influenza	N	Casesa	Vaccinated cases			Controlsb	Vaccinated controls			Overall IVE		Overall IVE (adjuvanted vaccine)		Overall IVE (non-adjuvanted vaccine)
			Adjuvanted vaccine	Non-adjuvanted vaccine	Total		Adjuvanted vaccine	Non-adjuvanted vaccine	Total	IVE	95% CI	IVE	95% CI	IVE	95% CI
All influenzac	1,477	483	100	140	240	994	239	271	510	9.86	−15.47 to 29.63	9.97	−24.43 to 34.86	7.82	−23.15 to 31.00
A(H1N1)pdm09d	684	77	12	16	28	607	137	189	326	48.33	13.51 to 69.13	34.38	−34.58 to 68.00	54.12	15.32 to 75.14
A(H3N2)e	1,226	232	54	77	131	994	239	271	510	−29.88	−79.09 to 5.81	−23.93	−87.94 to 18.28	−37.03	−98.15 to 5.24
B/Yamagataf	916	150	29	39	68	766	180	228	408	25.75	−8.83 to 49.35	30.09	−15.94 to 57.85	21.10	−24.43 to 49.97

CI: confidence interval; GP: general practitioner; IVE: influenza vaccine effectiveness; LCI: laboratory-confirmed influenza.

^a Cases in this column were individuals included in the study with LCI who were admitted to hospital during the period when influenza viruses of the type or subtype in question circulated. For example, cases of all influenza comprised all LCI individuals admitted during the 2017/18 influenza season, while cases of influenza A(H1N1)pdm09, A(H3N2) and B/Yamagata lineage only included patients admitted during times when influenza A(H1N1)pdm09, A(H3N2) and B/Yamagata lineage viruses respectively circulated. For each virus type, the time of circulation was estimated as the period between the first of at least two consecutive weeks with two or more cases of this type and the previous week of the first of two consecutive weeks with no cases of this type.

^b Controls in this column were individuals included in the study who tested negative for influenza in the laboratory and who were admitted to hospital during the time that viruses of the influenza type in question circulated. The time of circulation was estimated as described in the above footnote a.

^c Adjusted by age, number of chronic conditions, sex, socioeconomic class (occupation), admission in the last 12 months, number of GP visits in the last 3 months, smoking habits, obesity status, days between symptoms onset and swab, hospital and epidemiological week at admission. Nine individuals vaccinated with a vaccine different from the ones under study were excluded from the IVE estimations by vaccine type (seven controls and two cases).

^d Adjusted by age, sex and epidemiological week at admission. Four individuals vaccinated with a vaccine different from the ones under study were excluded from the IVE estimations by vaccine type; all four were controls.

^e Adjusted by age, number of chronic conditions, sex, socioeconomic status (occupation), admission in the last 12 months, number of GP visits in the last 3 months, smoking habits, obesity status, days between symptoms onset and swab, hospital and epidemiological week at admission. Eight individuals vaccinated with a vaccine different from the ones under study were excluded from the IVE estimations by vaccine type (seven controls and one case).

^f Adjusted by age, number of chronic conditions, sex, smoking habits and epidemiological week at admission. Seven individuals vaccinated with a vaccine different from the ones under study were excluded from the IVE estimations by vaccine type (six controls and one case).