FluWatch report: March 19 to April 1, 2023 (weeks 12-13)

On this page

• Influenza/Influenza-like Illness Activity - Geographic Spread
• Laboratory-Confirmed Influenza Detections
• Syndromic / Influenza-like Illness Surveillance
• Influenza Outbreak Surveillance
• Influenza Severe Outcomes Surveillance
• Influenza Strain Characterization
• Antiviral Resistance
• Influenza Vaccine Monitoring
• Provincial and International Surveillance Links

Influenza/Influenza-like Illness Activity - Geographic Spread

In week 13, 33 regions across Canada reported either sporadic or localized influenza activity (Figure 1). The number of regions reporting influenza activity and the intensity of reported activity remains stable. A total of 14 regions in Canada reported no activity this week.

Number of Regions Reporting in Week 13: 47 out of 53

Figure 1 - Text description

Province	Influenza Surveillance Region	Activity Level
N.L.	Eastern	Sporadic
N.L.	Labrador-Grenfell	No Activity
N.L.	Central	No Activity
N.L.	Western	No Activity
P.E.I.	Prince Edward Island	No Data
N.S.	Zone 1 - Western	No Activity
N.S.	Zone 2 - Northern	Sporadic
N.S.	Zone 3 - Eastern	No Activity
N.S.	Zone 4 - Central	No Activity
N.B.	Region 1	Sporadic
N.B.	Region 2	No Activity
N.B.	Region 3	Localized
N.B.	Region 4	Sporadic
N.B.	Region 5	No Activity
N.B.	Region 6	No Activity
N.B.	Region 7	Sporadic
Que.	Nord-est	Sporadic
Que.	Québec et Chaudieres-Appalaches	Sporadic
Que.	Centre-du-Québec	Sporadic
Que.	Montréal et Laval	Sporadic
Que.	Ouest-du-Québec	Sporadic
Que.	Montérégie	Sporadic
Ont.	Central East	Localized
Ont.	Central West	Sporadic
Ont.	Eastern	Sporadic
Ont.	North East	Sporadic
Ont.	North West	Sporadic
Ont.	South West	Localized
Ont.	Toronto	Localized
Man.	Northern Regional	No Activity
Man.	Prairie Mountain	Sporadic
Man.	Interlake-Eastern	Sporadic
Man.	Winnipeg	Sporadic
Man.	Southern Health	No Activity
Sask.	North	No Activity
Sask.	Central	No Activity
Sask.	South	Sporadic
Alta.	North Zone	Sporadic
Alta.	Edmonton	Sporadic
Alta.	Central Zone	Sporadic
Alta.	Calgary	Sporadic
Alta.	South Zone	Sporadic
B.C.	Interior	Sporadic
B.C.	Fraser	Sporadic
B.C.	Vancouver Coastal	Sporadic
B.C.	Vancouver Island	Sporadic
B.C.	Northern	No Activity
Y.T.	Yukon	Sporadic
N.W.T.	North	No Data
N.W.T.	South	No Data
Nvt.	Qikiqtaaluk	No Data
Nvt.	Kivalliq	No Data
Nvt.	Kitimeot	No Data

Laboratory-Confirmed Influenza Detections

In week 13, the weekly percentage of tests positive for influenza (2.4%) has increased slightly in recent weeks (from 0.8% in week 7) but remains at interseasonal levels. This weekly increase is due to the increase in the percentage of tests positive for influenza B.

The following results were reported from sentinel laboratories across Canada in week 13 (Figures 2 and 3):

• A total of 510 laboratory detections (364 influenza B and 146 influenza A) were reported. Influenza B detections (71%) are predominant.
• Among subtyped influenza A detections (24), 54% (13) were influenza A(H1N1).
• Among detections for which age information was reported (377), 307 (81%) of detections were in individuals aged under the age of 65 years.

To date this season (August 28, 2022 to April 1, 2023):

• 67,806 influenza detections were reported, of which 97% (65,737) were influenza A and among subtyped influenza A detections (20,587), influenza A(H3N2) accounted for 92% of detections.
• 49,198 laboratory-confirmed influenza detections with age information were reported, of which 19,968 (41%) were in individuals aged 0-19 years old (Figure 4).

For more detailed weekly and cumulative influenza data, see the text descriptions for Figures 2 and 3 or the Respiratory Virus Detections in Canada Report.

Number of Laboratories Reporting in Week 13: 33 out of 35

Figure 2 - Text description

Surveillance Week	A(Unsubtyped)	A(H3N2)	A(H1N1)	Influenza B	Percent Positive A	Percent Positive B
35	13	10	2	3	0.2	0.0
36	9	5	1	5	0.1	0.0
37	19	9	3	2	0.2	0.0
38	26	35	20	3	0.5	0.0
39	44	53	22	5	0.7	0.0
40	64	66	16	4	1.0	0.0
41	121	110	20	1	1.4	0.0
42	218	204	11	9	2.4	0.1
43	418	595	23	6	5.5	0.0
44	1055	1351	54	7	10.9	0.0
45	2026	2268	69	11	16.2	0.0
46	3453	2983	98	16	20.2	0.1
47	5916	2912	168	16	24.1	0.0
48	7372	2605	133	13	23.8	0.0
49	7028	2206	141	29	21.0	0.1
50	5686	1507	137	29	17.2	0.1
51	3776	849	155	19	12.5	0.1
52	2272	506	105	28	8.0	0.1
1	1338	316	86	29	4.6	0.1
2	553	139	54	18	2.2	0.1
3	326	47	49	44	1.4	0.1
4	172	40	42	42	0.9	0.2
5	154	25	35	80	0.8	0.3
6	138	18	30	94	0.7	0.3
7	98	11	31	75	0.6	0.3
8	102	20	20	127	0.6	0.5
9	109	18	30	182	0.6	0.7
10	109	10	26	201	0.6	0.8
11	89	7	25	296	0.5	1.2
12	104	3	29	311	0.6	1.3
13	122	11	13	364	0.7	1.7

The shaded area represents the maximum and minimum number of influenza tests or percentage of tests positive reported by week from seasons 2014-2015 to 2019-2020. Data from week 11 of the 2019-2020 season onwards are excluded from the historical comparison due to the COVID-19 pandemic.

The epidemic threshold is 5% tests positive for influenza. When it is exceeded, and a minimum of 15 weekly influenza detections are reported, a seasonal influenza epidemic is declared.

Figure 3 - Text description

Surveillance Week	Percentage of tests positive, 2022-2023	Percentage of tests positive, 2021-2022	Percentage of tests positive, 2020-2021	Maximum Percentage of Tests Positive	Minimum Percentage of Tests Positive	Average Percentage of Tests Positive
35	0.2	0.0	0.0	1.9	0.1	0.8
36	0.2	0.0	0.0	2.3	0.3	1.1
37	0.3	0.0	0.0	1.8	0.4	1.0
38	0.5	0.0	0.0	2.4	0.5	1.3
39	0.7	0.0	0.0	2.9	0.7	1.7
40	1.0	0.0	0.0	2.3	1.1	1.7
41	1.5	0.1	0.0	3.0	1.3	1.7
42	2.4	0.1	0.0	3.4	0.9	2.2
43	5.6	0.1	0.0	5.3	0.8	2.8
44	10.9	0.2	0.1	8.5	1.2	3.7
45	16.2	0.1	0.0	10.1	1.4	4.6
46	20.2	0.2	0.0	14.1	1.5	6.1
47	24.1	0.2	0.1	15.4	1.4	7.7
48	23.9	0.3	0.1	18.2	0.8	10.6
49	21.0	0.3	0.0	19.7	1.6	13.0
50	17.3	0.3	0.0	27.0	2.4	16.8
51	12.5	0.2	0.0	29.1	3.3	20.1
52	8.0	0.1	0.0	34.5	4.3	24.5
1	4.7	0.1	0.0	31.7	5.8	23.4
2	2.3	0.1	0.0	29.1	7.1	23.0
3	1.5	0.1	0.0	30.1	12.2	23.6
4	1.1	0.1	0.0	29.5	15.9	24.0
5	1.0	0.0	0.0	30.6	19.6	24.9
6	1.0	0.1	0.0	32.4	17.9	25.0
7	0.8	0.0	0.0	32.5	16.3	25.1
8	1.1	0.1	0.0	32.9	17.5	25.1
9	1.3	0.1	0.0	34.3	16.8	24.6
10	1.4	0.2	0.0	36.0	16.0	23.2
11	1.7	0.3	0.0	31.4	16.2	21.4
12	1.9	0.9	0.0	30.0	15.0	20.1
13	2.4	1.5	0.0	28.3	14.5	19.6
14	N/A	2.5	0.0	23.2	12.7	17.9
15	N/A	3.9	0.0	20.7	11.9	16.3
16	N/A	7.0	0.0	18.5	11.6	14.5
17	N/A	9.7	0.0	17.3	9.8	12.8
18	N/A	11.3	0.0	13.0	7.9	10.3
19	N/A	12.6	0.0	11.9	5.0	9.0
20	N/A	10.4	0.0	9.1	3.2	7.2
21	N/A	9.8	0.0	7.4	3.0	5.6
22	N/A	8.4	0.0	5.0	2.2	3.9
23	N/A	7.0	0.0	4.4	0.9	2.9
24	N/A	5.0	0.0	4.4	0.8	2.2
25	N/A	3.0	0.0	3.9	0.6	1.9
26	N/A	2.3	0.0	3.1	0.7	1.8
27	N/A	1.2	0.0	2.8	0.4	1.5
28	N/A	0.8	0.0	1.8	0.4	0.9
29	N/A	0.7	0.0	1.6	0.5	1.1
30	N/A	0.4	0.0	1.5	0.5	0.9
31	N/A	0.3	0.0	1.9	0.6	1.1
32	N/A	0.2	0.0	1.2	0.5	0.9
33	N/A	0.2	0.0	1.7	0.4	0.9
34	N/A	0.2	0.0	1.6	0.4	0.9

Laboratory data notes:

Testing for influenza and other respiratory viruses has been influenced by the current COVID-19 pandemic. Changes in laboratory testing practices may affect the comparability of data to previous seasons.

Due to different testing protocols of laboratories across Canada, some influenza A subtype detection counts may not be included in total influenza A detection counts and percent positivity calculations.

Figure 4 - Text description

a) Proportion of influenza A and B by age-group

Age Group	Proportion of Influenza A	Proportion of Influenza B	Total Number Influenza Detections
0 to 4	96.9%	3.1%	8731
5 to 19	96.2%	3.8%	11237
20 to 44	94.8%	5.2%	10169
45 to 64	97.8%	2.2%	6441
65+	99.3%	0.7%	12620

b) Proportion of subtyped influenza A(H1N1) and A(H3N2) by age-group

Age Group	Proportion of A(H1N1)	Proportion of A(H3N2)	Total Number of Subtyped Influenza Detections
0 to 4	5.6%	94.4%	2843
5 to 19	4.6%	95.4%	3573
20 to 44	9.2%	90.8%	2886
45 to 64	16.7%	83.3%	1855
65+	9.2%	90.8%	3604

Syndromic / Influenza-like Illness Surveillance

Healthcare Practitioners Sentinel Surveillance

In week 13, 1.1% of visits to healthcare professionals were due to influenza-like illness (ILI) (Figure 5). The percentage of visits for ILI is slightly below expected levels for this time of year.

ILI symptoms are not specific to any one respiratory pathogen and can be due to influenza, or other respiratory viruses, including respiratory syncytial virus and SARS-CoV-2, the virus that causes COVID-19. This makes the percentage of visits for ILI an important indicator of overall respiratory illness morbidity in the community in the presence of co-circulating viruses.

This indicator should be interpreted with caution as there have been changes in healthcare seeking behavior of individuals and a smaller number of sentinels reporting compared to previous seasons.

Number of Sentinels Reporting in Week 13: 36

The shaded area represents the maximum and minimum percentage of percentage of participants reporting cough and fever by week, from seasons 2014-2015 to 2019-2020. Data from week 11 of the 2019-2020 season onwards are excluded from the historical comparison due to the COVID-19 pandemic.

Figure 5 - Text description

Surveillance Week	2022-2023	2021-2022	2020-2021	Average	Min	Max
35	0.6%	0.6%	0.1%	0.6%	0.4%	0.9%
36	0.9%	1.2%	0.2%	0.6%	0.4%	0.9%
37	0.7%	0.6%	0.4%	0.7%	0.5%	1.0%
38	0.8%	0.9%	0.3%	0.7%	0.6%	1.0%
39	1.0%	1.0%	0.4%	0.9%	0.5%	1.2%
40	0.7%	0.5%	0.2%	1.2%	0.8%	1.7%
41	1.9%	1.1%	0.4%	1.7%	0.8%	2.8%
42	1.4%	1.2%	0.5%	1.6%	1.2%	2.1%
43	1.6%	0.9%	0.3%	1.2%	0.8%	1.7%
44	1.5%	0.6%	0.3%	1.2%	0.7%	1.7%
45	2.2%	1.0%	0.4%	1.2%	0.9%	1.5%
46	2.3%	0.9%	0.8%	1.4%	1.2%	1.8%
47	3.5%	0.7%	0.3%	1.6%	1.1%	2.2%
48	3.2%	1.1%	0.5%	1.5%	1.1%	2.2%
49	3.2%	0.9%	0.5%	1.7%	1.0%	2.8%
50	2.4%	1.1%	0.4%	1.5%	1.1%	1.7%
51	1.7%	1.7%	0.5%	1.9%	1.4%	2.7%
52	2.9%	1.5%	0.5%	2.0%	1.0%	3.1%
1	1.6%	2.1%	0.7%	3.4%	1.9%	5.4%
2	1.4%	1.6%	0.4%	3.4%	1.8%	5.7%
3	1.7%	1.4%	0.2%	2.3%	1.3%	3.7%
4	1.0%	0.9%	0.3%	2.0%	1.1%	2.9%
5	1.3%	1.0%	0.2%	2.1%	1.4%	3.1%
6	1.0%	0.7%	0.5%	2.4%	1.4%	4.0%
7	0.7%	0.7%	0.3%	2.4%	0.9%	3.5%
8	0.8%	0.8%	0.2%	2.3%	0.8%	3.4%
9	0.9%	0.7%	0.2%	2.3%	0.9%	3.1%
10	0.7%	0.9%	0.2%	2.0%	1.0%	2.8%
11	0.9%	0.6%	0.2%	1.9%	1.1%	2.8%
12	0.8%	0.8%	0.3%	1.6%	0.6%	2.6%
13	1.1%	1.2%	0.4%	1.6%	1.1%	2.6%
14	N/A	1.1%	0.2%	1.7%	1.1%	3.0%
15	N/A	1.2%	0.3%	1.3%	0.9%	1.9%
16	N/A	1.5%	0.3%	1.2%	0.8%	1.7%
17	N/A	1.3%	0.4%	1.2%	0.7%	1.7%
18	N/A	1.8%	0.5%	1.3%	0.5%	2.0%
19	N/A	1.7%	0.3%	0.9%	0.6%	1.3%
20	N/A	1.5%	0.5%	1.1%	0.6%	1.5%
21	N/A	1.4%	0.3%	0.9%	0.5%	1.3%
22	N/A	1.0%	0.3%	0.7%	0.3%	1.0%
23	N/A	1.1%	0.2%	0.8%	0.6%	1.0%
24	N/A	1.3%	0.2%	0.7%	0.6%	1.0%
25	N/A	1.0%	0.2%	0.6%	0.4%	0.8%
26	N/A	0.8%	0.2%	0.8%	0.5%	1.4%
27	N/A	1.7%	0.3%	0.6%	0.5%	0.7%
28	N/A	1.0%	0.1%	0.7%	0.5%	1.3%
29	N/A	0.9%	0.3%	0.9%	0.6%	1.7%
30	N/A	1.3%	0.2%	0.6%	0.2%	0.9%
31	N/A	0.9%	0.2%	0.4%	0.2%	0.6%
32	N/A	0.9%	0.2%	0.8%	0.3%	1.2%
33	N/A	0.8%	0.3%	0.7%	0.4%	1.3%
34	N/A	1.0%	0.5%	0.7%	0.4%	1.5%

FluWatchers

In week 13, 9,531 participants reported to FluWatchers, of which 1.5% reported symptoms of cough and fever (Figure 6). The percentage of FluWatchers who have reported cough and fever is below seasonal levels.

The reports of cough and fever are not specific to any one respiratory pathogen and can be due to influenza, or other respiratory viruses, including respiratory syncytial virus, rhinovirus, and SARS-CoV-2, the virus that causes COVID-19. This makes the proportion of individuals reporting cough and fever an important indicator of overall respiratory illness activity in the community in the presence of co-circulating viruses.

FluWatchers reporting is not impacted by changes in health services or health seeking behaviours.

Among the 142 participants who reported cough and fever:

• 23% consulted a healthcare professional.
• 78% reported days missed from work or school, resulting in an average of 2.9 missed days from work or school among those 111 participants.

The Northwest Territories had the highest participation rate this week (54 participants per 100,000 population) and the neighbourhood with postal code, K0A had the highest number of participants (119). See what is happening in your neighbourhood! Downloadable datasets are also available on Open Maps.

If you are interested in becoming a FluWatcher, sign up today.

Number of Participants Reporting in Week 13: 9,531

The shaded area represents the maximum and minimum percentage of percentage of participants reporting cough and fever by week, from seasons 2014-2015 to 2019-2020. Data from week 11 of the 2019-2020 season onwards are excluded from the historical comparison due to the COVID-19 pandemic.

Figure 6 - Text description

Surveillance Week	2022-2023	2021-2022	2020-2021	Average	Min	Max
35	1.3%	0.2%	0.2%	N/A	N/A	N/A
36	1.2%	0.3%	0.2%	N/A	N/A	N/A
37	1.6%	0.5%	0.4%	N/A	N/A	N/A
38	1.8%	0.5%	0.3%	N/A	N/A	N/A
39	2.3%	0.5%	0.4%	N/A	N/A	N/A
40	2.4%	0.6%	0.5%	2.5%	2.2%	2.7%
41	2.0%	0.5%	0.4%	2.2%	1.8%	2.6%
42	2.0%	0.4%	0.3%	1.8%	1.6%	2.0%
43	2.3%	0.5%	0.2%	1.9%	1.5%	2.2%
44	2.6%	0.5%	0.3%	1.6%	1.4%	1.8%
45	3.0%	0.5%	0.3%	1.8%	1.4%	2.3%
46	2.9%	0.4%	0.3%	1.8%	1.2%	2.2%
47	3.1%	0.6%	0.3%	1.9%	1.4%	2.4%
48	3.1%	0.5%	0.3%	2.4%	1.7%	3.4%
49	2.7%	0.4%	0.2%	2.6%	2.0%	3.2%
50	2.1%	0.6%	0.1%	2.9%	2.1%	3.8%
51	2.4%	1.0%	0.2%	3.2%	2.5%	3.9%
52	2.1%	1.5%	0.1%	4.0%	2.8%	5.4%
1	1.7%	1.1%	0.1%	3.8%	2.9%	4.8%
2	1.3%	1.0%	0.2%	2.9%	1.9%	3.9%
3	1.3%	0.8%	0.1%	3.3%	2.3%	4.8%
4	1.2%	0.6%	0.1%	3.1%	2.1%	4.2%
5	1.1%	0.6%	0.2%	3.2%	2.6%	3.6%
6	1.4%	0.5%	0.1%	3.5%	2.8%	4.3%
7	1.3%	0.4%	0.2%	3.2%	2.6%	3.8%
8	1.3%	0.5%	0.1%	3.1%	2.5%	3.6%
9	1.4%	0.5%	0.1%	2.8%	2.4%	3.5%
10	1.5%	0.6%	0.2%	2.6%	2.1%	3.1%
11	1.5%	0.9%	0.2%	2.3%	1.9%	2.6%
12	1.3%	1.2%	0.2%	2.6%	2.5%	2.8%
13	1.5%	1.8%	0.2%	2.5%	2.0%	3.1%
14	N/A	2.3%	0.2%	2.1%	1.3%	2.6%
15	N/A	1.9%	0.2%	1.8%	1.6%	1.9%
16	N/A	1.9%	0.1%	2.0%	1.5%	2.4%
17	N/A	1.6%	0.2%	1.7%	1.4%	2.3%
18	N/A	1.4%	0.2%	1.5%	1.2%	2.1%
19	N/A	1.3%	0.1%	N/A	N/A	N/A
20	N/A	1.2%	0.2%	N/A	N/A	N/A
21	N/A	1.2%	0.1%	N/A	N/A	N/A
22	N/A	1.2%	0.1%	N/A	N/A	N/A
23	N/A	1.2%	0.1%	N/A	N/A	N/A
24	N/A	1.3%	0.1%	N/A	N/A	N/A
25	N/A	1.3%	0.1%	N/A	N/A	N/A
26	N/A	1.8%	0.2%	N/A	N/A	N/A
27	N/A	2.0%	0.1%	N/A	N/A	N/A
28	N/A	1.9%	0.2%	N/A	N/A	N/A
29	N/A	1.8%	0.2%	N/A	N/A	N/A
30	N/A	1.6%	0.2%	N/A	N/A	N/A
31	N/A	1.3%	0.2%	N/A	N/A	N/A
32	N/A	1.2%	0.3%	N/A	N/A	N/A
33	N/A	1.4%	0.3%	N/A	N/A	N/A
34	N/A	1.3%	0.5%	N/A	N/A	N/A

Influenza Outbreak Surveillance

In week 13, one laboratory-confirmed influenza A outbreak in a LTC facility was reported.

To date this season (August 28, 2022 to April 1, 2023):

• 616 laboratory-confirmed influenza outbreaks have been reported
  • 333 were in LTC facilities (54%)
  • 174 were in facilities categorized as 'other' (28%)
  • 98 were in acute care facilities (16%)
  • 7 were in remote and/or isolated communities (<1%)
  • 4 were in schools/daycares (<1%)
  • All but three outbreaks were due to influenza A and among those with subtyping information (227), 92% were due to influenza A(H3N2)
• 287 ILI outbreaks have been reported
  • All but 3 ILI outbreaks have been reported in schools and/or daycares.

Outbreaks of ILI are not specific to any one respiratory pathogen and can be due influenza, or other respiratory viruses, including respiratory syncytial virus, rhinovirus, COVID-19, or a mixture of viruses. Many respiratory viruses in addition to the flu commonly circulate during the fall and winter, and can cause clusters of cases with respiratory illness which could be captured as ILI.

Number of provinces and territories^{Footnote 1} reporting in Week 13: 10 out of 13

Figure 7 - Text description

Surveillance Week	Acute Care Facilities	Long Term Care Facilities	Other	Schools and Daycares	Remote and/or Isolated Communities
35	0	0	1	0	0
36	0	1	0	0	0
37	0	0	0	0	0
38	1	1	0	0	0
39	0	2	1	0	0
40	0	3	4	0	0
41	1	2	1	0	0
42	3	0	2	0	0
43	1	7	6	3	0
44	1	10	12	1	0
45	13	27	10	0	0
46	12	37	18	0	0
47	15	38	17	0	7
48	13	44	22	0	0
49	10	53	25	0	0
50	10	32	16	0	0
51	3	24	10	0	0
52	2	20	10	0	0
1	2	17	6	0	0
2	5	5	6	0	0
3	1	0	1	0	0
4	1	0	1	0	0
5	0	5	1	0	0
6	0	2	0	0	0
7	0	0	1	0	0
8	0	1	0	0	0
9	2	0	0	0	0
10	0	0	0	0	0
11	2	0	3	0	0
12	0	1	0	0	0
13	0	1	0	0	0

Influenza Severe Outcomes Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

In week 13, nine influenza-associated hospitalizations were reported by participating provinces and territories^{Footnote 2}.

To date this season (August 28, 2022 to April 1, 2023), 4,008 influenza-associated hospitalizations were reported by participating provinces and territories:

• 99% of the hospitalizations were associated with influenza A.
• Of the cases with subtype information (2,047), 88% were associated with influenza A(H3N2)
• The highest cumulative hospitalization rates up to week 13 were among adults 65 years of age and older (132/100,000 population) and children under 5 years of age (123/100,000 population).

To date this season (August 28, 2022 to April 1, 2023), 336 ICU admissions and 267 influenza-associated deaths were reported.

• Adults aged 45-64 years of age and 65 years of age and older accounted for 29% and 32% of reported ICU admissions respectively.
• Adults aged 65 years of age and older accounted for 76% of reported deaths.

Number of provinces and territories reporting in Week 13: 7 out of 9

Figure 8 - Text description

Surveillance Week	0-4 yrs	5-19 yrs	20-44 yrs	45-64 yrs	65+ yrs	Overall
35	0.2	0.1	0.0	0.0	0.1	0.1
36	0.2	0.1	0.0	0.0	0.3	0.1
37	0.2	0.1	0.0	0.1	0.6	0.2
38	0.2	0.1	0.0	0.1	0.7	0.2
39	0.2	0.1	0.0	0.1	1.1	0.3
40	0.2	0.1	0.1	0.2	1.1	0.3
41	0.2	0.1	0.1	0.2	1.7	0.4
42	0.7	0.1	0.2	0.4	2.0	0.6
43	2.7	1.2	0.4	0.9	3.4	1.3
44	8.7	3.1	1.0	1.9	6.3	2.9
45	19.7	6.3	2.2	4.4	16.0	6.8
46	35.6	9.4	4.2	6.8	29.0	11.7
47	56.1	14.9	7.0	11.7	46.7	19.0
48	73.1	17.9	10.3	17.1	68.6	26.6
49	89.7	21.0	12.5	22.1	87.4	33.3
50	102.9	23.1	15.0	25.3	102.3	38.6
51	110.3	23.8	16.1	27.1	112.2	41.6
52	114.3	24.0	16.6	28.6	119.8	43.8
1	116.5	24.2	16.9	29.8	125.5	45.3
2	117.6	24.3	17.1	30.2	127.5	45.9
3	118.1	24.7	17.2	30.5	128.3	46.2
4	118.8	24.8	17.3	30.6	129.0	46.4
5	119.2	25.0	17.4	30.8	129.4	46.7
6	119.4	25.1	17.5	31.0	129.9	46.9
7	119.9	25.1	17.5	31.1	130.0	47.0
8	120.5	25.1	17.7	31.3	130.3	47.1
9	120.5	25.1	17.8	31.4	130.5	47.2
10	121.0	25.3	17.9	31.4	130.7	47.4
11	121.9	25.5	18.0	31.5	130.9	47.5
12	122.6	25.6	18.1	31.7	131.1	47.7
13	123.1	25.7	18.2	31.7	131.5	47.9

Pediatric Influenza Hospitalizations and Deaths

In week 13, fifteen influenza-associated pediatric (≤16 years of age) hospitalizations were reported by the Immunization Monitoring Program Active (IMPACT) network (Figure 9). Fourteen of the weekly hospitalizations were due to influenza B. Less than five influenza-associated ICU admissions were reported in week 13. No influenza-associated pediatric deaths have been reported since week 50 (mid December).

To date this season (August 28, 2022 to April 1, 2023):

• 1,589 pediatric influenza-associated hospitalizations have been reported.
• 97% of the hospitalizations were associated with influenza A.
• Children aged between 2-4 years and 5-9 years account for 55% of the reported pediatric hospitalizations (Figure 10).
• 214 ICU admissions were reported; children aged between 2-4 years and 5-9 years account for 55% of the reported pediatric ICU admissions.
• 8 influenza-associated pediatric deaths have been reported.

The shaded area represents the maximum and minimum number of hospitalizations, from seasons 2014-2015 to 2019-2020. Data from week 11 of the 2019-2020 season onwards are excluded from the historical comparison due to the COVID-19 pandemic.

Figure 9 - Text description

Surveillance week	2022-2023	2021-2022	Average	Min	Max
35	1	0	0	0	1
36	1	0	1	0	2
37	0	0	1	0	2
38	1	0	1	0	2
39	1	0	1	0	3
40	1	0	1	0	2
41	4	0	2	0	3
42	7	0	3	0	7
43	42	0	4	1	11
44	94	0	6	1	21
45	146	0	9	2	36
46	193	0	12	1	37
47	224	1	12	1	35
48	242	1	19	2	46
49	203	1	22	3	41
50	160	0	32	4	54
51	100	2	44	5	82
52	50	1	66	14	120
1	26	1	63	21	114
2	7	0	49	12	94
3	11	0	51	27	82
4	6	0	58	34	93
5	9	0	59	25	120
6	3	0	60	15	113
7	4	0	59	17	118
8	8	1	65	25	134
9	7	1	58	12	151
10	7	0	54	17	135
11	8	0	51	16	118
12	8	0	39	13	87
13	15	8	32	15	66
14	N/A	7	29	12	56
15	N/A	18	25	11	56
16	N/A	19	23	11	41
17	N/A	23	19	9	37
18	N/A	48	16	8	28
19	N/A	36	11	5	19
20	N/A	29	10	0	18
21	N/A	32	6	4	9
22	N/A	14	6	1	9
23	N/A	16	3	1	7
24	N/A	12	3	1	6
25	N/A	9	2	0	5
26	N/A	6	1	0	3
27	N/A	3	1	0	2
28	N/A	7	1	0	2
29	N/A	2	1	0	3
30	N/A	3	1	0	1
31	N/A	1	0	0	0
32	N/A	0	0	0	0
33	N/A	1	0	0	2
34	N/A	0	1	0	2

Figure 10 - Text description

Age Group	Total
0-5 mo	179
6-23 mo	291
2-4 yr	488
5-9 yr	392
10-16 yr	239

Influenza Strain Characterization

Since September 1, 2022, the National Microbiology Laboratory (NML) has characterized 437 influenza viruses (390 A(H3N2), 35 A(H1N1), and 12 influenza B) received from Canadian laboratories.

Genetic Characterization of Influenza A(H3N2)

Five influenza A(H3N2) viruses did not grow to sufficient hemagglutination titers for antigenic characterization by hemagglutination inhibition (HI) assays. Therefore, NML has performed genetic characterization to determine the genetic group identity of these viruses.

Sequence analysis of the HA genes of the viruses showed that they belonged to genetic group 3C.2a1b.2a2.

A/Darwin/6/2021 (H3N2)-like virus is an influenza A/H3N2 component of the 2022-23 Northern Hemisphere influenza vaccine and belongs to genetic group 3C.2a1b.2a2.

Antigenic Characterization

Influenza A(H3N2)

• Of the 385 influenza A (H3N2) viruses characterized, 379 were characterized as antigenically similar to A/Darwin/6/2021 (H3N2)-like virus with antisera raised against cell-grown A/Darwin/6/2021 (H3N2)-like virus. Six viruses showed reduced titer with antisera raised against cell-grown A/Darwin/6/2021 (H3N2)-like virus.
  • A/Darwin/6/2021 (H3N2)-like virus is an influenza A/H3N2 component of the 2022-23 Northern Hemisphere influenza vaccine.
• The 385 influenza A(H3N2) viruses characterized belonged to genetic group 3C.2a1b.2a2.

Influenza A(H1N1)

• 35 influenza A (H1N1) viruses were characterized as antigenically similar to A/Wisconsin/588/2019-like with ferret antisera produced against cell-propagated A/Wisconsin/588/2019.
  • A/Wisconsin/588/2019 is the influenza A/H1N1 component of the 2022-23 Northern Hemisphere influenza vaccine.

Influenza B

• 12 viruses characterized were antigenically similar to B/Austria/1359417/2021.
• Influenza B viruses can be divided into two antigenically distinct lineages represented by B/Yamagata/16/88 and B/Victoria/2/87 viruses.
  • The recommended influenza B components for the 2022-23 Northern Hemisphere influenza vaccine are B/Austria/1359417/2021 (Victoria lineage) and B/Phuket/3073/2013 (Yamagata lineage).

Antiviral Resistance

The NML also tests influenza viruses received from Canadian laboratories for antiviral resistance.

Oseltamivir

384 influenza viruses (346 A(H3N2), 32 A(H1N1) and 6 influenza B) were tested for resistance to oseltamivir and it was found that:

• All influenza viruses were sensitive to oseltamivir.

Zanamivir

384 influenza viruses (346 A(H3N2), 32 A(H1N1) and 6 influenza B) were tested for resistance to zanamivir and it was found that:

• All influenza viruses were sensitive to zanamivir.

Influenza Vaccine Monitoring

Vaccine monitoring refers to activities related to the monitoring of influenza vaccination coverage and vaccine effectiveness.

Vaccination Coverage

The Seasonal Influenza Immunization Vaccination Coverage Survey is an annual telephone survey conducted between January and February that collects information from Canadians on whether they received the annual seasonal influenza vaccine that season. Vaccination coverage is measured as the percentage of people who reported receiving the influenza vaccine in a specific influenza season.

In the 2022-2023 influenza season, coverage was slightly higher compared to the 2021-2022 season at:

• 44% among all adults aged 18 years and older.
  • 31% among adults aged 18-64 without chronic medical conditions.
  • 43% among adults aged 18-64 with chronic medical conditions.
• 74% among seniors (aged 65 years and older).

Table 1 – Seasonal influenza vaccination coverage, by risk group and influenza season, Seasonal Influenza Vaccination Coverage Survey, Canada, 2020-2021 to 2022-2023

Flu Season
	2022-2023		2021-2022		2020-2021
Age group (years)	n	Vaccination coverage % (95% CI)	n	Vaccination coverage % (95% CI)	n	Vaccination coverage % (95% CI)
All adults (≥18)	3535	43.5 (41.6-45.3)	3487	38.7 (36.9-40.6)	3014	40.4 (38.4-42.4)
18-64, without chronic medical condition	1715	31.0 (28.6-33.4)	1658	26.8 (24.4-29.2)	1498	29.2 (26.6-31.8)
18-64, with chronic medical condition	583	43.1 (38.6-47.6)	713	37.6 (33.6-41.7)	646	40.5 (36.2-44.8)
Seniors (≥65)	1198	73.7 (71.0-76.5)	1098	71.0 (68.1-74.0)	862	70.4 (67.1-73.8)

Vaccine Effectiveness

The Canadian Sentinel Practitioner Surveillance Network (SPSN) provides estimates of the effectiveness of the seasonal influenza vaccine in preventing medically-attended illness due to laboratory-confirmed influenza among Canadians.

Based on data collected between November 1, 2022 and January 6, 2023, vaccine effectiveness (VE) was estimated to be 54% against influenza A(H3N2). Due to the dominant circulation of influenza A(H3N2) this season, the VE estimate was only available for one influenza subtype. By age group, VE was 47% (95% CI 11 to 69) for individuals under the age of 19 years, 58% (95% CI 33 to 73) for adults aged 20-64 years and 59% (95% CI 15 to 80) for adults 65 years and older. The SPSN interim estimates are published and available online.

Updated influenza VE estimates, if available, will be published at the end of the 2022-2023 influenza season.

Provincial and International Surveillance Links

See Influenza surveillance resources

Notes

The data in the FluWatch report represent surveillance data available at the time of writing. All data are preliminary and may change as updates are received.

To learn more about the FluWatch program, see the Overview of influenza monitoring in Canada page.

For more information on the flu, see our Flu (influenza) web page.

We would like to thank all the FluWatch surveillance partners participating in this year's influenza surveillance program.

This report is available on the Government of Canada Influenza webpage.

Ce rapport est disponible dans les deux langues officielles.