Table 1. Participant profile, influenza A analyses, Canadian Sentinel Practitioner Surveillance Network, 29 October 2023–13 January 2024 (n = 3,095).

Characteristics	All ARI participants (column %)							Influenza-vaccinateda (row %, unless otherwise specified)
	Overall		Influenza A cases		Influenza controls		p valueb	Overall		p valuec	Influenza A casesd		Influenza controlsd
	n	%	n	%	n	%		n	%		n	%	n	%
N (row %)	3,095	100	722	23	2,373	77	NA	823	27	NA	115	16	708	30
Age group (years)e
1–8	546	18	150	21	396	17	< 0.001	85	16	< 0.001	13	9	72	18
9–19	317	10	80	11	237	10		48	15		11	14	37	16
20–49	1,151	37	293	41	858	36		217	19		36	12	181	21
50–64	568	18	125	17	443	19		166	29		27	22	139	31
65–79	407	13	65	9	342	14		226	56		22	34	204	60
≥ 80	106	3	9	1	97	4		81	76		6	67	75	77
Median (IQR)	39 (16–58)		35 (13–52)		40 (17–60)		< 0.001	57 (34–71)		< 0.001	47 (26–64)		58 (35–71)
Sex
Female	1,868	60	410	57	1,458	61	0.044	527	28	0.007	72	18	455	31
Male	1,208	39	303	42	905	38		288	24		41	14	247	27
Unknown	19	1	9	1	10	0	NA	8	42	NA	2	22	6	60
Comorbidityf
No	2,055	66	520	72	1,535	65	< 0.001	428	21	< 0.001	66	13	362	24
Yes	693	22	129	18	564	24		294	42		37	29	257	46
Unknown	347	11	73	10	274	12	NA	101	29	NA	12	16	89	32
Meets ILI criteria
No	136	4	16	2	120	5	< 0.001	29	21	0.202	1	6	28	23
Yes	2,483	80	636	88	1,847	78		652	26		104	16	548	30
Unknown	476	15	70	10	406	17	NA	142	30	NA	10	14	132	33
Province
Alberta	369	12	120	17	249	10	< 0.001	98	27	< 0.001	23	19	75	30
BC	419	14	84	12	335	14		180	43		25	30	155	46
Ontario	1,502	49	371	51	1,131	48		386	26		58	16	328	29
Quebec	805	26	147	20	658	28		159	20		9	6	150	23
Specimen collection interval from onset of ARIg
≤ 4 days	2,090	68	548	76	1,542	65	< 0.001	534	26	0.059	94	17	440	29
5–7 days	1,005	32	174	24	831	35		289	29		21	12	268	32
Weeks of specimen collection, 2023/24g
44–47	816	26	84	12	732	31	< 0.001	142	17	< 0.001	11	13	131	18
48–51	1,466	47	405	56	1,061	45		409	28		68	17	341	32
52–2	813	26	233	32	580	24		272	33		36	15	236	41
XBB.1.5 vaccination (any, without regard to timing), restricted to BC, Ontario and Quebec only (all column %)h
Totali	2,726	88	602	83	2,124	90	NA	725	88	NA	92	80	633	89
Yes	428	16	61	10	367	17	< 0.001	373	51	< 0.001	45	49	328	52
No	2,142	79	503	84	1,639	77		311	43		39	42	272	43
Unknown	156	6	38	6	118	6	NA	41	6	NA	8	9	33	5

ARI: acute respiratory illness; BC: British Columbia; ILI: Influenza like illness; IQR: interquartile range; NA: not applicable; SPSN: Canadian Sentinel Practitioner Surveillance Network.

^a Vaccination status based on participant or guardian report. Participants vaccinated < 2 weeks before onset of symptoms or with unknown vaccination status or timing were excluded.

^b p values for comparison between cases and controls were derived by two-way chi-squared test or Wilcoxon rank-sum test.

^c p values for comparison between vaccinated and not vaccinated were derived by two-way chi-squared test or Wilcoxon rank-sum test. The number not vaccinated can be derived by subtracting the number vaccinated from the total ARI participants, by row.

^d Without regard to time before illness onset, 131 of 738 (18%) cases and 814 of 2,479 (33%) controls across the analysis period were vaccinated (p < 0.001).

^e Children < 1 year excluded as per usual in prior SPSN analyses based on variability and/or uncertainty in their age-related vaccine eligibility over the course of the epidemic. Other age strata defined as per usual SPSN analyses predicated upon one- and two-dose recommendations for children ≥ 9 and < 9 years, respectively; higher likelihood of chronic comorbidity at ≥ 50 years; and higher age-associated risk among adults ≥ 65 years [31].

^f Includes chronic comorbidities that place individuals at higher risk of serious complications from influenza as defined by Canada’s National Advisory Committee on Immunization [31].

^g Missing specimen collection dates were imputed as the date the specimen was received and processed at the laboratory minus 2 days.

^h XBB.1.5 vaccination status based on provincial immunisation registry data from BC, Ontario and Quebec.

ⁱ Total participants from BC, Ontario and Quebec, including those with unknown XBB.1.5 vaccination status used in the derivation of percentages displayed in all succeeding rows.