Table 1
Interim vaccine effectiveness (VE) estimates against influenza, Canadian Sentinel Practitioner Surveillance Network (SPSN), 1 November 2019–1 February 2020 (n = 2,808)
Influenza outcome	Age group (years)	Total	Cases			Controls			Adjusted VE %^a,b,c	95% CI
Influenza outcome	Age group (years)	Total	All	Vaccinated	%	All	Vaccinated	%	Adjusted VE %^a,b,c	95% CI
Any A or B^d	All ages	2,808	1,411	191	14	1,397	399	29	58	47 to 66
	1–19	866	512	33	6	354	70	20	74	59 to 84
	20–64	1,718	841	122	15	877	229	26	55	41 to 66
	≥65^e	224	58	36	62	166	100	60	18	−59 to 58
Influenza A	All ages	2,128	731	131	18	1,397	399	29	49	34 to 60
	1–19	543	189	15	8	354	70	20	70	44 to 84
	20–64	1,372	495	88	18	877	229	26	45	25 to 59
	≥65	213	47	28	ND	166	100	60	NE
A(H1N1)pdm09	All ages	1,948	551	107	19	1,397	399	29	44	26 to 58
	1–19	478	124	13	10	354	70	20	63	25 to 81
	20–64	1,273	396	75	19	877	229	26	39	14 to 56
	≥65	197	31	19	ND	166	100	60	NE
A(H3N2)	All ages	1,561	164	22	13	1,397	399	29	62	37 to 77
	1–19	414	60	2	3	354	70	20	NE
	20–64	967	90	11	12	877	229	26	64	29 to 81
	≥65	180	14	9	ND	166	100	60	NE
Influenza B^f	All ages	2,080	683	60	9	1,397	399	29	69	57 to 77
	1–19	679	325	18	6	354	70	20	77	59 to 87
	20–64	1,224	347	34	10	877	229	26	68	51 to 79
	≥65	177	11	8	ND	166	100	60	NE
CI: confidence interval; ND: not displayed owing to small denominator; NE: not estimated owing to sparse data; VE: vaccine effectiveness. ^a All VE estimates adjusted for age group, province (Alberta, British Columbia, Ontario, Quebec), specimen collection interval (≤ 4; 5–7 days) and calendar time (modelled as a natural cubic spline with three equally-spaced knots). For all ages, age group adjustment based on 1–8, 9–19, 20–49, 50–64 and ≥ 65 years. For children 1–19 years old, age adjustment based on 1–8 and 9–19 years. For adults 20–64 years old, age adjustment based on 20–49 and 50–64 years. ^b Additional adjustment for comorbidity (yes/no/unknown) and sex (male/female/unknown) did not alter any of the displayed VE estimates by more than 2% (absolute) except where specified. ^c Using a later study start date of 1 December 2019 did not alter any of the displayed VE estimates by more than 3% (absolute). ^d Excluding the province of British Columbia where a smaller proportion of doses distributed were quadrivalent, the VE estimate for all ages was unchanged and age-stratified estimates remained within 6% (absolute) of those displayed. ^e With additional adjustment for comorbidity (yes/no/unknown) and sex (male/female/unknown), VE was 14% (95% CI: −71 to 57). ^f Excluding the province of British Columbia, none of the influenza B VE estimates were higher and all remained within 5% (absolute) of those displayed.