Table 3. Pooled adjusted seasonal vaccine effectiveness against influenza A(H3N2), by previous vaccination status, among those aged ≥ 9 years and by age group, by clade and genetic variants, I-MOVE primary care multicentre study, Europe, influenza season 2018/19 (n = 3,983).

Age group	Outcome	Previous vaccination status	Cases	Controls	Adjusted VE (%)	95% CI (%)
≥ 9 years	A(H3N2)	Not vaccinated in either season	1,147	2,061	Ref
		Vaccinated in 2018/19 only	76	99	−27	−81 to 11
		Vaccinated in 2017/18 only	25	113	45	11 to 66
		Vaccinated in both seasons	153	309	5	−23 to 27
15–64 years	A(H3N2)	Not vaccinated in either season	852	1,719	Ref
		Vaccinated in 2018/19 only	46	59	−43	−121 to 7
		Vaccinated in 2017/18 only	17	79	46	5 to 70
		Vaccinated in both seasons	69	116	−14	−62 to 20
≥ 65 years	A(H3N2)	Not vaccinated in either season	91	152	Ref
		Vaccinated in 2018/19 only	24	36	22	−62 to 63
		Vaccinated in 2017/18 only	5	30	48	−55 to 83
		Vaccinated in both seasons	78	184	31	−9 to 56
≥ 9 years	Clade 3C.2a1b	Not vaccinated in either season	209	1,492	Ref
		Vaccinated in 2018/19 only	12	80	−14	−132 to 44
		Vaccinated in 2017/18 only	4	74	ND^a
		Vaccinated in both seasons	36	203	49	17 to 69
≥ 9 years	Clade 3C.3a	Not vaccinated in either season	94	930	Ref
		Vaccinated in 2018/19 only	6	58	−34	−248 to 49
		Vaccinated in 2017/18 only	3	42	ND^a
		Vaccinated in both seasons	20	163	−122	−353 to −9

^a Omitted because of small sample size.

CI: confidence interval; ND: not done; Ref: reference value; VE: vaccine effectiveness.