FluWatch report: May 5 to May 11 2024 (week 19)

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Organization: Public Health Agency of Canada

Published: 2024-05-17

Weekly highlights

At the national level, indicators of influenza activity are decreasing and are within or below expected levels typical of this time of year. The percentage of tests positive for influenza fell below 5% this week. This suggests that Canada is nearing the end of the 2023-2024 influenza season at the national level.

Virologic

  • In week 19, the percentage of tests positive for influenza was 4.2% and a total of 1,077 laboratory detections (238 influenza A and 839 influenza B) were reported.

Syndromic

  • The percentage of FluWatchers reporting cough and fever was 1.0% in week 19. The percentage of FluWatchers reporting cough and fever remains below expected levels for this time of year.

Outbreaks

  • From August 27, 2023 to May 11, 2024 (weeks 35 to 19), 1,207 laboratory-confirmed influenza outbreaks have been reported (2 laboratory-confirmed influenza outbreaks were reported in week 19).

Severe Outcomes

  • From August 27, 2023 to May 11, 2024 (weeks 35 to 19), 4,386 influenza-associated hospitalizations were reported by participating provinces and territories. Adults aged 65 years of age and older accounted for 45% of reported hospitalizations. The highest cumulative hospitalization rates were among adults 65 years of age and older (134/100,000) and children under 5 years of age (98/100,000).
  • From October 1, 2023 to May 11, 2024 (weeks 40 to 19), 1,111 influenza-associated pediatric hospitalizations were reported from a total of 4,641 positive influenza tests across ten sentinel hospital sites.

Other Notes

On this page

Influenza/influenza-like illness activity - Geographic spread

In week 19, 7 regions in one province reported localized influenza activity (Ont.) and 30 regions across Canada reported sporadic influenza activity. 5 regions in three province and territories reported no activity this week (N.B., N.W.T., and Nvt.). (Figure 1).

Figure 1 - Map of influenza/ILI activity by province and territory, Canada, week 2024-19

Number of Regions Reporting in week 19: 42 out of 53

Figure 1. Text version below.
Figure 1 - Text description
Province Influenza Surveillance Region Activity Level
N.L. Eastern Sporadic
N.L. Labrador-Grenfell Sporadic
N.L. Central Sporadic
N.L. Western Sporadic
P.E.I. Prince Edward Island Sporadic
N.S. Zone 1 - Western Sporadic
N.S. Zone 2 - Northern Sporadic
N.S. Zone 3 - Eastern Sporadic
N.S. Zone 4 - Central Sporadic
N.B. Region 1 Sporadic
N.B. Region 2 Sporadic
N.B. Region 3 Sporadic
N.B. Region 4 No Activity
N.B. Region 5 No Activity
N.B. Region 6 Sporadic
N.B. Region 7 No Activity
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 Localized
Ont. South West Localized
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 Sporadic
Sask. South Sporadic
Alta. North Zone Sporadic
Alta. Edmonton Sporadic
Alta. Central Zone Sporadic
Alta. Calgary Sporadic
Alta. South Zone Sporadic
B.C. Interior No Data
B.C. Fraser No Data
B.C. Vancouver Coastal No Data
B.C. Vancouver Island No Data
B.C. Northern No Data
Y.T. Yukon No Data
N.W.T. North No Activity
N.W.T. South Sporadic
Nvt. Qikiqtaaluk Sporadic
Nvt. Kivalliq Sporadic
Nvt. Kitimeot No Activity

Laboratory-confirmed influenza detections

Influenza percent positivity continues to decrease (1,077 detections, 4.2%). The following results were reported from sentinel laboratories across Canada in week 19 (Figures 2 and 3):

To date this season (August 27, 2023 to May 11, 2024):

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 2024-19

Number of Laboratories Reporting in Week 19: 35 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 27 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 74 20 0.5 0.1
40 39 20 80 13 0.6 0.1
41 42 9 51 7 0.5 0.0
42 59 15 96 19 0.7 0.1
43 99 29 136 23 1.2 0.1
44 291 52 315 25 2.6 0.1
45 684 61 541 37 4.9 0.1
46 1032 103 961 47 7.2 0.2
47 1147 134 1321 35 8.8 0.1
48 1668 156 1901 85 11.6 0.3
49 2277 194 2327 99 14.7 0.3
50 2899 236 2662 139 15.3 0.4
51 3880 330 2650 184 16.8 0.5
52 4851 395 2465 220 18.2 0.5
1 4111 442 1771 259 14.5 0.6
2 3204 337 872 225 11.2 0.6
3 2643 222 636 279 10.3 0.8
4 3058 111 469 380 11.1 1.1
5 3273 146 360 524 11.3 1.5
6 2910 116 335 593 10.4 1.7
7 2680 118 253 740 9.4 2.2
8 2226 78 224 1054 8.0 3.2
9 1740 113 204 1311 6.7 4.0
10 1396 91 187 1622 5.6 5.1
11 995 59 167 1656 4.4 5.4
12 712 58 146 1782 3.3 5.8
13 588 42 122 1971 2.7 6.6
14 494 56 96 2040 2.3 6.8
15 368 55 76 1775 1.8 6.0
16 240 52 68 1356 1.4 5.0
17 161 48 90 1260 1.2 4.7
18 169 63 55 1133 1.1 4.2
19 120 28 61 839 0.9 3.3
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 2024-19
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 2.7 10.8 0.2 8.4 1.2 3.7
45 5.1 16.2 0.1 10.1 1.4 4.6
46 7.4 20.3 0.2 14.1 1.5 6.0
47 8.9 24.3 0.2 15.4 1.4 7.7
48 11.9 24.1 0.3 18.2 0.8 10.6
49 15.0 21.2 0.3 19.3 1.6 12.9
50 15.7 17.4 0.3 27.0 2.4 16.4
51 17.2 12.5 0.2 29.1 3.3 20.0
52 18.7 8.0 0.1 34.5 4.3 24.4
1 15.1 4.6 0.1 31.7 5.9 23.5
2 11.7 2.3 0.1 29.1 7.1 23.0
3 11.1 1.5 0.1 30.1 12.2 23.7
4 12.2 1.1 0.1 29.5 15.9 24.0
5 12.8 1.0 0.0 30.6 19.6 24.9
6 12.1 1.0 0.0 32.4 17.9 25.0
7 11.6 0.9 0.0 32.5 16.3 25.1
8 11.2 1.1 0.1 32.9 17.6 25.2
9 10.8 1.3 0.1 34.3 16.8 24.4
10 10.7 1.4 0.2 36.0 16.1 23.3
11 9.8 1.7 0.3 31.4 16.2 21.4
12 9.1 1.9 0.9 30.0 15.0 20.1
13 9.3 2.4 1.5 28.3 14.5 19.6
14 9.0 2.2 2.5 26.2 12.7 19.1
15 7.8 2.5 3.9 20.7 12.0 16.3
16 6.3 2.4 7.0 18.5 11.6 14.5
17 5.9 2.4 9.7 17.3 9.8 12.8
18 5.3 2.3 11.3 13.0 7.9 10.3
19 4.2 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 2024-18
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 B Total Number Influenza Detections
0 to 4 78.3% 21.7% 10955
5 to 19 57.1% 42.9% 13683
20 to 44 69.2% 30.8% 17282
45 to 64 90.6% 9.4% 14798
65+ 96.4% 3.6% 21388
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 89.7% 10.3% 2876
5 to 19 87.1% 12.9% 2885
20 to 44 82.8% 17.2% 4058
45 to 64 91.1% 8.9% 4134
65+ 81.9% 18.1% 5491

Syndromic / influenza-like illness surveillance

Healthcare practitioners sentinel surveillance

Sentinel practitioner ILI surveillance data will not be updated further due to the limited number of reporting sentinels.

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 2024-12
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 1.2% 1.0% 0.4% 1.2% 0.9% 1.5%
46 2.0% 0.9% 0.8% 1.4% 1.2% 1.8%
47 1.7% 0.7% 0.3% 1.6% 1.1% 2.2%
48 2.0% 1.1% 0.5% 1.5% 1.1% 2.2%
49 2.0% 0.9% 0.5% 1.7% 1.0% 2.8%
50 2.2% 1.1% 0.4% 1.5% 1.1% 1.7%
51 2.0% 1.7% 0.5% 1.9% 1.4% 2.7%
52 1.8% 1.5% 0.5% 2.0% 1.0% 3.1%
1 1.8% 2.1% 0.7% 3.4% 1.9% 5.4%
2 2.4% 1.6% 0.4% 3.4% 1.8% 5.7%
3 1.3% 1.4% 0.2% 2.3% 1.3% 3.7%
4 1.6% 0.9% 0.3% 2.0% 1.1% 2.9%
5 2.1% 1.0% 0.2% 2.1% 1.4% 3.1%
6 1.7% 0.7% 0.5% 2.4% 1.4% 4.0%
7 1.6% 0.7% 0.3% 2.4% 0.9% 3.5%
8 1.3% 0.8% 0.2% 2.3% 0.8% 3.4%
9 1.4% 0.7% 0.2% 2.3% 0.9% 3.1%
10 1.8% 0.9% 0.2% 2.0% 1.0% 2.8%
11 1.6% 0.6% 0.2% 1.9% 1.1% 2.8%
12 2.3% 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 19, 8,534 participants reported to FluWatchers, of which 1.0% reported symptoms of cough and fever (Figure 6). The percentage of FluWatchers reporting cough and fever remains below 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 87 participants who reported cough and fever:

The Yukon had the highest participation rate this week (55 participants per 100,000 population) and the neighbourhood with postal code K0A had the highest number of participants (110). 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 2024-19

Number of Participants Reporting in Week 19: 8,534

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 1.9% 2.9% 0.4% 1.8% 1.2% 2.2%
47 2.0% 3.1% 0.6% 1.9% 1.4% 2.4%
48 2.2% 3.1% 0.5% 2.4% 1.7% 3.4%
49 2.2% 2.7% 0.4% 2.6% 2.0% 3.2%
50 2.5% 2.1% 0.6% 2.9% 2.1% 3.8%
51 2.4% 2.4% 1.0% 3.2% 2.5% 3.9%
52 3.0% 2.1% 1.5% 4.0% 2.8% 5.4%
1 2.2% 1.7% 1.1% 3.8% 2.9% 4.8%
2 1.4% 1.3% 1.0% 2.9% 1.9% 3.9%
3 1.4% 1.3% 0.8% 3.3% 2.3% 4.8%
4 1.5% 1.2% 0.6% 3.1% 2.1% 4.2%
5 1.5% 1.1% 0.6% 3.2% 2.6% 3.6%
6 1.6% 1.4% 0.5% 3.5% 2.8% 4.3%
7 1.6% 1.3% 0.4% 3.2% 2.6% 3.8%
8 1.4% 1.3% 0.5% 3.1% 2.5% 3.6%
9 1.3% 1.4% 0.5% 2.8% 2.4% 3.5%
10 1.3% 1.5% 0.6% 2.6% 2.1% 3.1%
11 1.3% 1.5% 0.9% 2.3% 1.9% 2.6%
12 1.2% 1.3% 1.2% 2.6% 2.5% 2.8%
13 1.5% 1.5% 1.8% 2.5% 2.0% 3.1%
14 1.4% 1.3% 2.3% 2.1% 1.3% 2.6%
15 1.0% 1.4% 1.9% 1.8% 1.6% 1.9%
16 1.2% 1.2% 1.9% 2.0% 1.5% 2.4%
17 1.2% 1.2% 1.6% 1.7% 1.4% 2.3%
18 1.1% 1.1% 1.4% 1.5% 1.2% 2.1%
19 1.0% 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 19, 2 laboratory-confirmed influenza outbreaks were reported.

To date this season (August 27, 2023 to May 11, 2024):

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.

Figure 7 - Number of new outbreaks of laboratory-confirmed influenza by report week, Canada, weeks 2023-35 to 2024-19

Number of provinces and territoriesFootnote 1 reporting in week 19: 10 out of 13

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 3 1 0 0
44 2 6 2 0 0
45 1 2 5 0 0
46 8 4 1 0 0
47 6 5 7 0 0
48 8 12 6 0 0
49 12 23 10 0 0
50 13 24 18 0 0
51 11 24 18 0 0
52 6 50 18 0 0
1 31 67 22 0 0
2 27 60 22 0 0
3 22 35 11 0 0
4 53 64 12 0 0
5 26 40 13 0 0
6 17 27 9 0 0
7 13 27 11 0 0
8 13 28 8 1 0
9 18 23 9 0 0
10 8 23 5 0 0
11 5 15 4 0 0
12 6 14 2 0 0
13 4 18 10 0 0
14 6 11 5 0 0
15 2 7 1 0 0
16 2 5 4 0 0
17 3 7 1 0 0
18 2 6 0 1 0
19 0 1 1 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 19, 26 influenza-associated hospitalizations, no ICU admissions, and no influenza-associated deaths were reported by participating provinces and territoriesFootnote 2.

To date this season (August 27, 2023 to May 11, 2024), 4,386 influenza-associated hospitalizations were reported by participating provinces and territories:

To date this season (August 27, 2023 to May 11, 2024), 484 ICU admissions and 247 influenza-associated deaths were reported.

Figure 8 - Cumulative rates of influenza-associated hospitalizations by age-group and surveillance week, Canada, participating provinces and territories, week 2023-35 to 2024-19

Number of provinces and territories reporting in week 19: 5 out of 5

Figure 8. Text version below.

Figure 8 - Text description
Surveillance Week 0-4 yrs 5-19 yrs 20-44 yrs 45-64 yrs 65+ yrs Overall
35 - 0.1 - 0.0 0.2 0.0
36 - 0.1 - 0.0 0.4 0.1
37 - 0.1 - 0.2 0.7 0.2
38 - 0.1 0.0 0.2 0.8 0.2
39 0.4 0.1 0.1 0.3 1.1 0.3
40 0.4 0.1 0.1 0.4 1.6 0.5
41 0.4 0.3 0.2 0.5 1.9 0.6
42 0.9 0.4 0.2 0.6 2.1 0.7
43 0.9 0.7 0.3 0.9 2.9 1.0
44 2.7 1.1 0.5 1.4 4.7 1.7
45 4.3 1.7 0.9 2.5 7.8 2.8
46 9.2 2.4 1.6 4.5 13.1 4.9
47 16.4 3.7 2.6 7.7 19.5 7.7
48 24.4 5.7 4.2 12.1 28.2 11.7
49 36.6 7.4 6.3 17.2 41.9 17.0
50 44.9 9.5 8.3 22.6 57.4 22.6
51 52.5 11.8 9.8 28.0 71.5 27.7
52 59.0 13.2 11.3 32.8 87.0 32.7
1 62.4 13.9 12.2 36.5 99.6 36.4
2 65.7 14.2 12.7 38.1 105.1 38.2
3 67.5 14.4 13.0 39.4 110.0 39.6
4 69.1 15.1 13.4 40.3 113.5 40.8
5 70.2 15.6 13.6 41.2 117.1 41.9
6 71.8 16.0 14.0 42.0 119.0 42.6
7 72.2 16.4 14.2 42.4 120.1 43.1
8 74.0 17.0 14.5 43.0 121.7 43.8
9 76.5 17.5 14.9 43.3 123.2 44.6
10 78.7 18.5 15.4 43.8 124.9 45.4
11 81.0 19.7 15.8 44.2 126.2 46.2
12 84.8 20.6 16.2 44.7 127.2 47.0
13 86.8 21.5 16.6 45.1 128.4 47.7
14 89.0 22.5 17.3 45.7 129.9 48.6
15 92.0 23.0 17.8 46.2 131.0 49.4
16 94.0 23.5 18.0 46.6 131.5 49.8
17 95.8 23.9 18.5 46.9 132.2 50.4
18 96.4 24.4 18.9 47.1 133.1 50.9
19 98.3 24.7 19.3 47.4 134.1 51.4
20 - - - - - -
21 - - - - - -
22 - - - - - -
23 - - - - - -
24 - - - - - -
25 - - - - - -
26 - - - - - -
27 - - - - - -
28 - - - - - -
29 - - - - - -
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34 - - - - - -

Sentinel Pediatric Influenza Severe Outcomes

For the 2023-2024 season, data on pediatric influenza associated severe outcomes are provided by the Surveillance Program for Rapid Identification and Tracking of Infectious Diseases in kids (SPRINT-KIDS) NetworkFootnote 3. The SPRINT-KIDS sentinel pediatric (≤18 years) hospital network provides severe outcome monitoring in both the emergency department and inpatient facilities and consists of 15 pediatric hospitals across 8 provinces in Canada (all provinces with the exception of New Brunswick and Prince Edward Island).

Emergency and Inpatient Influenza Testing

In week 19, 1,635 tests were conducted for influenza in emergency departments and inpatient wards from 11/15 sites:

To date this season (October 1, 2023 to May 11, 2024):

Hospitalizations

In week 19, 9 influenza-associated pediatric hospitalizations were reported from a total of 113 positive influenza tests from 10/15 sites:

To date this season (October 1, 2023 to May 11, 2024):

Influenza strain characterization

Since September 1, 2023, the National Microbiology Laboratory Branch (NMLB) has characterized 1,685 influenza viruses (294 A(H3N2), 822 A(H1N1), and 569 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, NML has genetically characterized 1,699 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 846 2a 398 The A(H1N1) component belongs to genetic clade 6B.1A.5a.2a.1
2a.1 477
A(H3N2) 3C.2a1b.2a 258 2a.1b 3 The A(H3N2) component belongs to genetic clade 3C.2a1b.2a.2a
2a.3a 1
2a.3a.1 283
B/Victoria V1A 460 3a.2 537 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 has not yet reported antiviral resistance results for influenza viruses collected during the 2023-2024 season.

Oseltamivir

1,318 influenza viruses (212 H3N2, 757 H1N1 and 349 influenza B) were tested for resistance to oseltamivir.

Zanamivir

1,318 influenza viruses (212 H3N2, 757 H1N1 and 349 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

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 2023-2024 influenza season, coverage was similar to previous seasons (2022-2023; 2019-2020):

Table 2: Seasonal influenza vaccination coverage, by risk group and influenza season, Seasonal Influenza Vaccination Coverage Survey, Canada, 2020-2021 to 2023-2024
Age group (years) Flu Season
2023-2024 2022-2023 2021-2022 2020-2021
n Vaccination coverage
% (95%CI)
n Vaccination coverage
% (95%CI)
n Vaccination coverage
% (95% CI)
n Vaccination coverage
% (95% CI)
All adults (≥18) 5344 42.2 (40.5-44.0) 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 2264 28.5 (26.1-30.8) 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 987 44.1 (40.1-48.1) 583 43.1 (38.6-47.6) 713 37.6 (33.6-41.7) 646 40.5 (36.2-44.8)
Seniors (≥65) 2072 72.7 (70.3-75.1) 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) provided mid-season 2023/24 vaccine effectiveness (VE) estimates for the multivalent influenza and monovalent Omicron XBB.1.5 vaccines in preventing medically-attended illness due to laboratory-confirmed influenza and COVID-19 among Canadians.

During the analysis period, influenza A made up >95% of influenza viruses. Among influenza A viruses, 80% were H1N1 and 20% were H3N2. The SPSN applied whole genome sequencing (WGS) to genetically characterize about 70% of all contributing influenza viruses. Among characterized H1N1 viruses they found a roughly equal proportion of vaccine matched clade 5a.2a.1 and alternate 5a.2a viruses. Among H3N2 detections, virtually all belonged to clade 2a.3a.1, genetically distinct from the clade 2a vaccine strain.

Based on data collected between October 29, 2023 and January 13, 2024, VE was estimated to be 63% (95% CI: 51-72) overall against influenza A(H1N1) and 40% (95% C:I 5-61) against influenza A(H3N2). VE was lower for H1N1 viruses belonging to clade 5a.2a.1 than 5a.2a and the SPSN provides possible reasons for that in the publication. Influenza A (H1N1) VE estimates were higher in children <20 years at 68% (95% CI: 42 to 83) and older adults 65 years and older at 72% (95% CI: 47 to 85), compared to adults 20-64 years at 56% (95% CI: 38 to 69); however, confidence intervals in age-stratified analyses broadly overlapped. Owing to limited detection of influenza A(H3N2) or influenza B viruses, age-stratified A(H3N2) and influenza B VE estimates were not reported in mid-season analyses.

The SPSN interim estimates are published and available online. Updated influenza VE estimates, inclusive of further age stratification and for influenza B will be published, if feasible, at the end of the 2023-2024 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.

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.

Return to footnote 1 referrer

Footnote 2

Influenza-associated hospitalizations are reported by Alberta, New Brunswick, Newfoundland and Labrador, Prince Edward Island and Yukon.

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Footnote 3

Sentinel pediatric severe outcome surveillance data was previously provided by the Immunization Monitoring Program ACTive (IMPACT) network. The change in the sentinel network will affect the comparability of pediatric hospitalization data from the 2023-2024 season to previous seasons as the number of hospitalizations (weekly and cumulative) may appear higher due to a greater number of sentinel sites.

Return to footnote 3 referrer

Footnote 4

Represents total number of sites reporting this data to date this season; some sites may not have reported data every week.

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