FluWatch report: November 5 to November 11, 2023 (week 45)

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Organization: Public Health Agency of Canada

Published: 2023-11-17

Weekly highlights

At the national level, influenza activity increased this week but overall activity remains below the seasonal threshold. Sporadic influenza activity continues to be reported in many regions across Canada and the number of regions reporting localized activity is increasing.

Virologic

  • In week 45, the percentage of tests positive for influenza was 4.3% and a total of 1,071 laboratory detections (1,038 influenza A and 33 influenza B) were reported.

Syndromic

  • The percentage of visits for influenza-like illness (ILI) was 1.3% in week 45. The percentage of visits for ILI is within levels typical of this time of year.
  • The percentage of FluWatchers reporting cough and fever was 1.9% in week 45. The percentage of FluWatchers reporting cough and fever is within levels typical of this time of year.

Outbreaks

  • From August 27, 2023 to November 11, 2023 (weeks 35 to 45), 32 laboratory-confirmed influenza outbreaks have been reported (7 laboratory-confirmed influenza outbreaks were reported in week 45).

Severe Outcomes

  • From August 27, 2023 to November 11, 2023 (weeks 35 to 45), 184 influenza-associated hospitalizations were reported by participating provinces and territories. Adults aged 65 years of age and older accounted for 51% of reported hospitalizations.

Other notes

On this page

Influenza/influenza-like illness activity - Geographic spread

In week 45, 24 regions across Canada reported sporadic influenza activity and 12 regions in six provinces reported localized influenza activity (N.L., N.S., Ont., Sask., Alta., and B.C.) (Figure 1). The number of regions reporting influenza activity and the intensity of reported activity is increasing. A total of 11 regions in Canada reported no activity this week.

Figure 1 – Map of influenza/ILI activity by province and territory, Canada, week 2023-45

Number of Regions Reporting in week 45: 47 out of 53

Figure 1. Text version below.
Figure 1 - Text description
Province Influenza Surveillance Region Activity Level
N.L. Eastern Localized
N.L. Labrador-Grenfell No Activity
N.L. Central Localized
N.L. Western Sporadic
P.E.I. Prince Edward Island No Data
N.S. Zone 1 - Western Sporadic
N.S. Zone 2 - Northern Localized
N.S. Zone 3 - Eastern Sporadic
N.S. Zone 4 - Central Sporadic
N.B. Region 1 Sporadic
N.B. Region 2 No Activity
N.B. Region 3 No Activity
N.B. Region 4 No Activity
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 Localized
Ont. Eastern Localized
Ont. North East Localized
Ont. North West Sporadic
Ont. South West Sporadic
Ont. Toronto Localized
Man. Northern Regional No Data
Man. Prairie Mountain No Data
Man. Interlake-Eastern No Data
Man. Winnipeg No Data
Man. Southern Health No Data
Sask. North Sporadic
Sask. Central Localized
Sask. South Localized
Alta. North Zone Sporadic
Alta. Edmonton Sporadic
Alta. Central Zone Sporadic
Alta. Calgary Localized
Alta. South Zone Sporadic
B.C. Interior Sporadic
B.C. Fraser Sporadic
B.C. Vancouver Coastal Localized
B.C. Vancouver Island Sporadic
B.C. Northern Sporadic
Y.T. Yukon No Activity
N.W.T. North No Activity
N.W.T. South Sporadic
Nvt. Qikiqtaaluk No Activity
Nvt. Kivalliq No Activity
Nvt. Kitimeot No Activity

Laboratory-confirmed influenza detections

The weekly percentage of tests positive for influenza (4.3% in week 45) continues to increase but is within expected levels for this time of year. Influenza activity remains below the seasonal threshold.

The following results were reported from sentinel laboratories across Canada in week 45 (Figures 2 and 3):

To date this season (August 27, 2023 to November 11, 2023):

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.

Figure 2. Number of positive influenza tests and percentage of tests positive, by type, subtype and report week, Canada, week 2023-35 to 2023-45

Number of Laboratories Reporting in week 45: 34 out of 35

Figure 2. Text version below.
Figure 2 - Text description
Surveillance Week A(Unsubtyped) A(H3N2) A(H1N1) Influenza B Percent Positive A Percent Positive B
35 19 26 51 9 0.7 0.1
36 12 11 50 9 0.4 0.1
37 28 14 46 6 0.5 0.0
38 28 15 57 4 0.5 0.0
39 18 10 75 20 0.5 0.1
40 41 20 79 13 0.7 0.1
41 43 11 53 7 0.5 0.0
42 60 15 95 19 0.7 0.1
43 109 28 129 23 1.2 0.1
44 305 54 308 25 2.7 0.1
45 606 39 327 33 4.2 0.1
46 0 0 0 0 0.0 0.0
47 0 0 0 0 0.0 0.0
48 0 0 0 0 0.0 0.0
49 0 0 0 0 0.0 0.0
50 0 0 0 0 0.0 0.0
51 0 0 0 0 0.0 0.0
52 0 0 0 0 0.0 0.0
1 0 0 0 0 0.0 0.0
2 0 0 0 0 0.0 0.0
3 0 0 0 0 0.0 0.0
4 0 0 0 0 0.0 0.0
5 0 0 0 0 0.0 0.0
6 0 0 0 0 0.0 0.0
7 0 0 0 0 0.0 0.0
8 0 0 0 0 0.0 0.0
9 0 0 0 0 0.0 0.0
10 0 0 0 0 0.0 0.0
11 0 0 0 0 0.0 0.0
12 0 0 0 0 0.0 0.0
13 0 0 0 0 0.0 0.0
14 0 0 0 0 0.0 0.0
15 0 0 0 0 0.0 0.0
16 0 0 0 0 0.0 0.0
17 0 0 0 0 0.0 0.0
18 0 0 0 0 0.0 0.0
19 0 0 0 0 0.0 0.0
20 0 0 0 0 0.0 0.0
21 0 0 0 0 0.0 0.0
22 0 0 0 0 0.0 0.0
23 0 0 0 0 0.0 0.0
24 0 0 0 0 0.0 0.0
25 0 0 0 0 0.0 0.0
26 0 0 0 0 0.0 0.0
27 0 0 0 0 0.0 0.0
28 0 0 0 0 0.0 0.0
29 0 0 0 0 0.0 0.0
30 0 0 0 0 0.0 0.0
31 0 0 0 0 0.0 0.0
32 0 0 0 0 0.0 0.0
33 0 0 0 0 0.0 0.0
34 0 0 0 0 0.0 0.0
Figure 3. Percentage of tests positive in Canada compared to previous seasons, week 2023-35 to 2023-45
Figure 3. Text version below.

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, 2023-2024 Percentage of tests positive, 2022-2023 Percentage of tests positive, 2021-2022 Maximum Percentage of Tests Positive Minimum Percentage of Tests Positive Average Percentage of Tests Positive
35 0.8 0.2 0.0 1.9 0.1 0.8
36 0.5 0.2 0.0 2.3 0.3 1.1
37 0.5 0.3 0.0 1.8 0.4 1.0
38 0.5 0.5 0.0 2.4 0.6 1.3
39 0.6 0.7 0.0 3.0 0.6 1.7
40 0.7 1.0 0.0 2.3 1.1 1.7
41 0.5 1.4 0.1 3.0 1.3 1.7
42 0.8 2.4 0.1 3.4 0.9 2.2
43 1.3 5.5 0.1 5.3 0.8 2.8
44 2.8 10.8 0.2 8.4 1.2 3.7
45 4.3 16.2 0.1 10.1 1.4 4.6
46 - 20.3 0.2 14.1 1.5 6.0
47 - 24.3 0.2 15.4 1.4 7.7
48 - 24.1 0.3 18.2 0.8 10.6
49 - 21.2 0.3 19.3 1.6 12.9
50 - 17.4 0.3 27.0 2.4 16.4
51 - 12.5 0.2 29.1 3.3 20.0
52 - 8.0 0.1 34.5 4.3 24.4
1 - 4.6 0.1 31.7 5.9 23.5
2 - 2.3 0.1 29.1 7.1 23.0
3 - 1.5 0.1 30.1 12.2 23.7
4 - 1.1 0.1 29.5 15.9 24.0
5 - 1.0 0.0 30.6 19.6 24.9
6 - 1.0 0.0 32.4 17.9 25.0
7 - 0.9 0.0 32.5 16.3 25.1
8 - 1.1 0.1 32.9 17.6 25.2
9 - 1.3 0.1 34.3 16.8 24.4
10 - 1.4 0.2 36.0 16.1 23.3
11 - 1.7 0.3 31.4 16.2 21.4
12 - 1.9 0.9 30.0 15.0 20.1
13 - 2.4 1.5 28.3 14.5 19.6
14 - 2.2 2.5 26.2 12.7 19.1
15 - 2.5 3.9 20.7 12.0 16.3
16 - 2.4 7.0 18.5 11.6 14.5
17 - 2.4 9.7 17.3 9.8 12.8
18 - 2.3 11.3 13.0 7.9 10.3
19 - 2.1 12.6 12.0 5.0 9.0
20 - 2.1 10.4 9.1 3.2 7.2
21 - 1.6 9.8 7.5 3.0 5.6
22 - 1.6 8.4 4.9 2.2 3.9
23 - 1.3 7.0 4.4 0.9 2.9
24 - 1.1 5.0 4.4 0.8 2.3
25 - 1.0 3.0 4.0 0.6 1.9
26 - 0.7 2.3 3.0 0.7 1.8
27 - 0.6 1.2 2.8 0.4 1.4
28 - 0.8 0.8 1.8 0.4 0.9
29 - 0.5 0.7 1.5 0.5 1.1
30 - 0.5 0.4 1.5 0.5 0.9
31 - 0.5 0.3 1.9 0.6 1.1
32 - 0.7 0.2 1.2 0.5 0.9
33 - 0.7 0.2 1.7 0.4 0.9
34 - 0.6 0.2 1.6 0.4 0.9
Figure 4. Proportion of positive influenza specimens by type or subtype and age-group reported through case-based laboratory reporting, Canada, week 2023-35 to 2023-45
Figure 4. Text version below.

Laboratory data notes:

Testing for influenza and other respiratory viruses has been influenced by the 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 A Total Number Influenza Detections
0 to 4 95.0% 5.0% 358
5 to 19 91.5% 8.5% 472
20 to 44 92.6% 7.4% 530
45 to 64 98.1% 1.9% 523
65+ 97.4% 2.6% 697
b) Proportion of subtyped influenza A(H1N1) and A(H3N2) by age-group
Age Group Proportion of Influenza A Proportion of Influenza A Total Number Influenza Detections
0 to 4 87.7% 12.3% 146
5 to 19 92.4% 7.6% 211
20 to 44 80.7% 19.3% 233
45 to 64 90.4% 9.6% 219
65+ 79.3% 20.7% 319

Syndromic / influenza-like illness surveillance

Healthcare practitioners sentinel surveillance

In week 45, 1.3% of visits to healthcare professionals were due to influenza-like illness (ILI) (Figure 5). The percentage of visits for ILI has increased but is within 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 a smaller number of sentinels reporting compared to previous seasons.

Figure 5. Percentage of visits for ILI reported by sentinels by report week, Canada, weeks 2023-35 to 2023-45

Number of Sentinels Reporting in week 45: 36

Figure 5. Text version below.

The shaded area represents the maximum and minimum percentage of visits for ILI 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.

Figure 5 - Text description
Surveillance Week 2023-2024 2022-2023 2021-2022 Average Min Max
35 0.5% 0.6% 0.1% 0.6% 0.4% 0.9%
36 0.4% 1.2% 0.2% 0.6% 0.4% 0.9%
37 0.8% 0.6% 0.4% 0.7% 0.5% 1.0%
38 0.8% 0.9% 0.3% 0.7% 0.6% 1.0%
39 0.9% 1.0% 0.4% 0.9% 0.5% 1.2%
40 0.6% 0.5% 0.2% 1.2% 0.8% 1.7%
41 1.6% 1.1% 0.4% 1.7% 0.8% 2.8%
42 1.0% 1.2% 0.5% 1.6% 1.2% 2.1%
43 0.8% 0.9% 0.3% 1.2% 0.8% 1.7%
44 1.3% 0.6% 0.3% 1.2% 0.7% 1.7%
45 1.3% 1.0% 0.4% 1.2% 0.9% 1.5%
46 - 0.9% 0.8% 1.4% 1.2% 1.8%
47 - 0.7% 0.3% 1.6% 1.1% 2.2%
48 - 1.1% 0.5% 1.5% 1.1% 2.2%
49 - 0.9% 0.5% 1.7% 1.0% 2.8%
50 - 1.1% 0.4% 1.5% 1.1% 1.7%
51 - 1.7% 0.5% 1.9% 1.4% 2.7%
52 - 1.5% 0.5% 2.0% 1.0% 3.1%
1 - 2.1% 0.7% 3.4% 1.9% 5.4%
2 - 1.6% 0.4% 3.4% 1.8% 5.7%
3 - 1.4% 0.2% 2.3% 1.3% 3.7%
4 - 0.9% 0.3% 2.0% 1.1% 2.9%
5 - 1.0% 0.2% 2.1% 1.4% 3.1%
6 - 0.7% 0.5% 2.4% 1.4% 4.0%
7 - 0.7% 0.3% 2.4% 0.9% 3.5%
8 - 0.8% 0.2% 2.3% 0.8% 3.4%
9 - 0.7% 0.2% 2.3% 0.9% 3.1%
10 - 0.9% 0.2% 2.0% 1.0% 2.8%
11 - 0.6% 0.2% 1.9% 1.1% 2.8%
12 - 0.8% 0.3% 1.6% 0.6% 2.6%
13 - 1.2% 0.4% 1.6% 1.1% 2.6%
14 - 1.1% 0.2% 1.7% 1.1% 3.0%
15 - 1.2% 0.3% 1.3% 0.9% 1.9%
16 - 1.5% 0.3% 1.2% 0.8% 1.7%
17 - 1.3% 0.4% 1.2% 0.7% 1.7%
18 - 1.8% 0.5% 1.3% 0.5% 2.0%
19 - 1.7% 0.3% 0.9% 0.6% 1.3%
20 - 1.5% 0.5% 1.1% 0.6% 1.5%
21 - 1.4% 0.3% 0.9% 0.5% 1.3%
22 - 1.0% 0.3% 0.7% 0.3% 1.0%
23 - 1.1% 0.2% 0.8% 0.6% 1.0%
24 - 1.3% 0.2% 0.7% 0.6% 1.0%
25 - 1.0% 0.2% 0.6% 0.4% 0.8%
26 - 0.8% 0.2% 0.8% 0.5% 1.4%
27 - 1.7% 0.3% 0.6% 0.5% 0.7%
28 - 1.0% 0.1% 0.7% 0.5% 1.3%
29 - 0.9% 0.3% 0.9% 0.6% 1.7%
30 - 1.3% 0.2% 0.6% 0.2% 0.9%
31 - 0.9% 0.2% 0.4% 0.2% 0.6%
32 - 0.9% 0.2% 0.8% 0.3% 1.2%
33 - 0.8% 0.3% 0.7% 0.4% 1.3%
34 - 1.0% 0.5% 0.7% 0.4% 1.5%

FluWatchers

In week 45, 9,210 participants reported to FluWatchers, of which 1.9% reported symptoms of cough and fever (Figure 6). The percentage of FluWatchers reporting cough and fever has increased but is within expected levels for this time of year.

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 174 participants who reported cough and fever:

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 (122). 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.

Figure 6. Percentage of FluWatchers reporting cough and fever, Canada, week 2023-35 to 2023-45

Number of Participants Reporting in week 45: 9,210

Figure 6. Text version below.

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 2023-2024 2022-2023 2021-2022 Average Min Max
35 1.1% 1.3% 0.2% - - -
36 1.2% 1.2% 0.3% - - -
37 1.5% 1.6% 0.5% - - -
38 2.0% 1.8% 0.5% - - -
39 2.3% 2.3% 0.5% - - -
40 1.8% 2.4% 0.6% 2.5% 2.2% 2.7%
41 1.6% 2.0% 0.5% 2.2% 1.8% 2.6%
42 1.7% 2.0% 0.4% 1.8% 1.6% 2.0%
43 1.7% 2.3% 0.5% 1.9% 1.5% 2.2%
44 1.9% 2.6% 0.5% 1.6% 1.4% 1.8%
45 1.9% 3.0% 0.5% 1.8% 1.4% 2.3%
46 - 2.9% 0.4% 1.8% 1.2% 2.2%
47 - 3.1% 0.6% 1.9% 1.4% 2.4%
48 - 3.1% 0.5% 2.4% 1.7% 3.4%
49 - 2.7% 0.4% 2.6% 2.0% 3.2%
50 - 2.1% 0.6% 2.9% 2.1% 3.8%
51 - 2.4% 1.0% 3.2% 2.5% 3.9%
52 - 2.1% 1.5% 4.0% 2.8% 5.4%
1 - 1.7% 1.1% 3.8% 2.9% 4.8%
2 - 1.3% 1.0% 2.9% 1.9% 3.9%
3 - 1.3% 0.8% 3.3% 2.3% 4.8%
4 - 1.2% 0.6% 3.1% 2.1% 4.2%
5 - 1.1% 0.6% 3.2% 2.6% 3.6%
6 - 1.4% 0.5% 3.5% 2.8% 4.3%
7 - 1.3% 0.4% 3.2% 2.6% 3.8%
8 - 1.3% 0.5% 3.1% 2.5% 3.6%
9 - 1.4% 0.5% 2.8% 2.4% 3.5%
10 - 1.5% 0.6% 2.6% 2.1% 3.1%
11 - 1.5% 0.9% 2.3% 1.9% 2.6%
12 - 1.3% 1.2% 2.6% 2.5% 2.8%
13 - 1.5% 1.8% 2.5% 2.0% 3.1%
14 - 1.3% 2.3% 2.1% 1.3% 2.6%
15 - 1.4% 1.9% 1.8% 1.6% 1.9%
16 - 1.2% 1.9% 2.0% 1.5% 2.4%
17 - 1.2% 1.6% 1.7% 1.4% 2.3%
18 - 1.1% 1.4% 1.5% 1.2% 2.1%
19 - 0.9% 1.3% - - -
20 - 1.0% 1.2% - - -
21 - 0.9% 1.2% - - -
22 - 0.7% 1.2% - - -
23 - 0.9% 1.2% - - -
24 - 0.9% 1.3% - - -
25 - 0.7% 1.3% - - -
26 - 0.9% 1.8% - - -
27 - 0.8% 2.0% - - -
28 - 0.6% 1.9% - - -
29 - 0.6% 1.8% - - -
30 - 0.7% 1.6% - - -
31 - 1.0% 1.3% - - -
32 - 0.9% 1.2% - - -
33 - 0.9% 1.4% - - -
34 - 1.2% 1.3% - - -

Influenza outbreak surveillance

In week 45, seven laboratory-confirmed influenza outbreaks were reported.

To date this season (August 27, 2023 to November 11, 2023):

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.

Number of provinces and territoriesFootnote 1 reporting in week 45: 11 out of 13

Figure 7: Number of new outbreaks of laboratory-confirmed influenza by report week, Canada, weeks 2023-35 to 2023-45
Figure 7. Text version below.
Figure 7 - Text description
Surveillance Week Acute Care Facilities Long Term Care Facilities Other Schools and Daycares Remote and/or Isolated Communities
35 0 1 1 0 0
36 0 0 0 0 0
37 0 2 0 0 0
38 0 2 0 0 0
39 0 1 0 0 0
40 0 2 0 0 0
41 0 1 0 0 0
42 0 2 0 0 0
43 0 2 1 0 0
44 2 6 2 0 0
45 1 2 4 0 0
46 0 0 0 0 0
47 0 0 0 0 0
48 0 0 0 0 0
49 0 0 0 0 0
50 0 0 0 0 0
51 0 0 0 0 0
52 0 0 0 0 0
1 0 0 0 0 0
2 0 0 0 0 0
3 0 0 0 0 0
4 0 0 0 0 0
5 0 0 0 0 0
6 0 0 0 0 0
7 0 0 0 0 0
8 0 0 0 0 0
9 0 0 0 0 0
10 0 0 0 0 0
11 0 0 0 0 0
12 0 0 0 0 0
13 0 0 0 0 0
14 0 0 0 0 0
15 0 0 0 0 0
16 0 0 0 0 0
17 0 0 0 0 0
18 0 0 0 0 0
19 0 0 0 0 0
20 0 0 0 0 0
21 0 0 0 0 0
22 0 0 0 0 0
23 0 0 0 0 0
24 0 0 0 0 0
25 0 0 0 0 0
26 0 0 0 0 0
27 0 0 0 0 0
28 0 0 0 0 0
29 0 0 0 0 0
30 0 0 0 0 0
31 0 0 0 0 0
32 0 0 0 0 0
33 0 0 0 0 0
34 0 0 0 0 0

Influenza severe outcomes surveillance

Provincial/territorial influenza hospitalizations and deaths

In week 45, 42 influenza-associated hospitalizations, 8 ICU admissions, and less than 5 influenza-associated deaths were reported by participating provinces and territoriesFootnote 2.

To date this season (August 27, 2023 to November 11, 2023), 184 influenza-associated hospitalizations were reported by participating provinces and territories:

To date this season (August 27, 2023 to November 11, 2023), 21 ICU admissions and 6 influenza-associated deaths were reported.

Number of provinces and territories reporting in week 45: 7 out of 9

Pediatric influenza hospitalizations and deaths

Data for laboratory-confirmed influenza-associated pediatric (≤16 years of age) hospitalizations were not available for weeks 45.

Influenza strain characterization

Since September 1, 2023, the National Microbiology Laboratory Branch (NMLB) has characterized 79 influenza viruses (63 A(H1N1), 9 A(H3N2), and 7 influenza B) received from Canadian laboratories.

Antigenic Characterization

Changes in circulating influenza viruses are monitored by antigenic characterization. Antigenic characterization results show how similar the circulating viruses are to reference viruses. Reference viruses represent strains included in the current seasonal influenza vaccine.

Influenza A(H1N1)

A/Wisconsin/67/2022 is the influenza A(H1N1) component of the 2023-2024 Northern Hemisphere influenza vaccine.

Influenza A(H3N2)

A/Darwin/6/2021 (H3N2)-like virus is the influenza A(H3N2) component of the 2023-2024 Northern Hemisphere influenza vaccine.  

Influenza B

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 2023-2024 Northern Hemisphere influenza vaccine are B/Austria/1359417/2021 (Victoria lineage) and B/Phuket/3073/2013 (Yamagata lineage)

Genetic Characterization

Genetic characterization is used to determine how similar gene sequences of circulating influenza viruses are to the sequences of the vaccine components used in the current seasonal influenza vaccine.

Since September 1, 2023, NMLB has genetically characterized 70 influenza viruses.

Table 1: Genetic Characterizations results of influenza A(H3N2), influenza A(H1N1) and Influenza B, Canada, season 2023-2024
Virus Subtype or Lineage HA Clade Number of Viruses Characterized HA Subclade Number of viruses Characterized HA genetic clades and subclades of the 2023-2024 Northern Hemisphere influenza vaccine components
A(H1N1) 6B.1A.5a 57 2a 14 The A(H1N1) component belongs to genetic clade 6B.1A.5a.2a.1
2a.1 43
A(H3N2) 3C.2a1b.2a 9 2a.3a.1 9 The A(H3N2) component belongs to genetic clade 3C.2a1b.2a.2a
B/Victoria V1A 4 3a.2 4 The B/Victoria component belongs to genetic clade V1A.3
B/Yamagata Y3 0 Y3 0 The B/Yamagata component belongs to genetic clade Y3

Antiviral resistance

The National Microbiology Laboratory Branch also tests influenza viruses received from Canadian laboratories for antiviral resistance.

Oseltamivir

70 influenza viruses (9 H3N2, 57 H1N1 and 4 influenza B) were tested for resistance to oseltamivir.

Zanamivir

70 influenza viruses (9 H3N2, 57 H1N1 and 4 influenza B) were tested for resistance to zanamivir.

Influenza vaccine monitoring

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

Vaccination coverage

Influenza vaccine coverage estimates for the 2023-2024 season are anticipated to be available in February or March 2024.

Vaccine effectiveness

Influenza vaccine effectiveness estimates for the 2023-2024 season are anticipated to be available in February or March 2024.

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.

Footnote 1

All Provinces and Territories (PTs) participate in the FluWatch outbreak surveillance system. This outbreak system monitors influenza and ILI outbreaks in long-term care facilities (LTCF), acute care facilities, schools and daycares, remote and/or isolated communities, and facilities categorized as 'other'. Not all reporting PTs report outbreaks in all these settings. All PTs report laboratory confirmed outbreaks in LTCF. Six PTs (AB, SK, NB, NS, PEI, and NL) report ILI outbreaks in schools and/or daycares and other facilities.

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Footnote 2

Influenza-associated hospitalizations are reported by Alberta, Manitoba, New Brunswick, Newfoundland and Labrador, Northwest Territories, Nova Scotia, Prince Edward Island and Yukon. Only hospitalizations that require intensive medical care are reported by Saskatchewan.

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