FluWatch report: July 19 to August 22, 2020 (weeks 30-34)

thumbnail

Download the alternative format
(PDF format, 1.2 MB, 15 pages)

Organization: Public Health Agency of Canada

Date published: 2020-06-15

Related Topics

Overall Summary

  • In weeks 30 to 34, exceptionally low levels of influenza activity were reported across Canada.
  • During weeks 30 to 34, the percentage of tests positive for influenza (0.03%) remained at the lowest level recorded for the past nine seasons.  The proportion of primary care visits for ILI were lower than average; no outbreaks and no influenza-related hospitalizations were reported.
  • Many influenza surveillance indicators may be influenced by the COVID-19 pandemic, including changes in healthcare-seeking behaviour, impacts of public health measures (e.g. social distancing) and influenza testing capacity. Current data should be interpreted with consideration for this context. See the COVID-19 Epidemiology update for information on COVID-19 cases in Canada.
  • This is the final FluWatch report of the 2019-2020 surveillance season. The first report of the 2020-2021 season will be published on September 25, 2020. Weekly reporting of laboratory detections of respiratory viruses will continue via our Respiratory Virus Detections Surveillance System.

Influenza/Influenza-like Illness (ILI) Activity (geographic spread)

During week 34, no influenza/ILI activity was reported in only one region in BC (Figure 1).

Figure 1 - Map of influenza/ILI activity by province and territory, Canada, week 2020-34

Number of Regions Reporting in week 34: 33 out of 53

Figure 1. Text equivalent follows.

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

Laboratory-Confirmed Influenza Detections

In weeks 30 to 34, the percentage of laboratory tests positive for influenza remained at the lowest level observed compared the past 9 seasons (Figure 2). The average percentage of tests positive for influenza during this 5-week period was  0.03% compared to 1.43% during the past 5 seasons.

In weeks 30-34, an average of 5,270 tests for influenza were performed at reporting laboratories, which is three times the average for this period over the past 5 seasons.

The percentage of positive tests crossed the seasonal threshold of 5% in week 12 (mid-March), indicating the end of the influenza season at the national level, 9 weeks earlier than average compared to the past 5 seasons. An abrupt end to the 2019-20 influenza season was observed in several countries, concurrent with the implementation of public health measures to reduce the spread of COVID-19.

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

To date this season (weeks 35 to 34), all influenza types and subtypes have circulated (Figure 3). Among the 55,378 laboratory detections of influenza reported:

Detailed information on age and type/subtype has been received for 42,541 laboratory-confirmed influenza cases (Table 1). To date this season (weeks 35 to 34):

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, weeks 2019-35 to 2020-34

Number of Laboratories Reporting in Week 34: 32 out of 36

Figure 2

The shaded area indicates weeks where the positivity rate was at least 5% and a minimum of 15 positive tests were observed, signalling the period of seasonal influenza activity.

Figure 2 - Text equivalent
Surveillance Week A(Unsubtyped) A(H3N2) A(H1N1) Influenza B Percent Positive A Percent Positive B
35 10 16 0 2 1.3 0.1
36 11 13 2 2 1.1 0.1
37 5 17 2 5 0.9 0.2
38 11 15 3 6 1.0 0.2
39 11 21 2 3 1.0 0.1
40 34 9 1 2 1.2 0.1
41 34 18 0 5 1.4 0.1
42 54 12 1 14 1.6 0.3
43 44 13 7 17 1.6 0.3
44 43 23 16 17 1.8 0.3
45 57 57 20 39 2.2 0.7
46 82 43 23 77 2.7 1.4
47 118 49 33 124 3.1 1.9
48 225 67 42 223 4.9 3.2
49 281 79 41 336 5.3 4.1
50 463 100 73 654 7.7 8.0
51 794 149 169 1094 10.6 10.4
52 1223 267 197 1439 15.0 12.7
1 1620 261 431 1533 15.8 10.3
2 1690 165 493 1463 15.8 9.4
3 1575 139 417 1418 16.2 10.3
4 1727 133 370 1952 15.2 12.7
5 1983 97 440 2269 16.0 13.7
6 1970 75 344 2265 15.6 14.1
7 1741 76 321 1851 15.5 12.8
8 1768 74 255 1559 16.3 11.6
9 1928 58 303 1287 16.7 8.9
10 1772 81 399 1152 13.6 6.5
11 1552 70 354 1015 9.8 4.3
12 832 38 154 595 4.8 2.5
13 185 19 39 269 1.3 1.2
14 48 5 11 97 0.3 0.4
15 14 1 7 19 0.1 0.1
16 1 0 3 11 0.0 0.1
17 5 1 0 14 0.0 0.1
18 4 0 0 9 0.0 0.1
19 0 0 0 12 0.0 0.1
20 6 0 0 11 0.1 0.1
21 1 0 1 9 0.0 0.1
22 5 0 0 4 0.1 0.0
23 2 0 3 2 0.1 0.0
24 0 0 0 2 0.0 0.0
25 3 0 0 1 0.1 0.0
26 0 0 0 0 0 0
27 1 0 1 0 0.0 0.0
28 1 0 0 1 0.0 0.0
29 1 0 0 3 0.0 0.0
30 0 0 0 2 0.0 0.0
31 0 0 0 1 0.0 0.0
32 0 0 0 0 0.0 0.0
33 2 0 1 3 0.1 0.1
34 0 0 0 0 0.0 0.0

Figure 3 - Distribution of positive influenza specimens by type/subtype and province/territory, Canada, weeks 2019-35 to 2020-34

Figure 3. Text equivalent follows.
Figure 3 - Text equivalent
ProvincesTable Figure 3 - Footnote 1 Cumulative (August 25, 2019 to July 18, 2020)
A Total A(H1N1) A(H3N2) A(UnS)Table Figure 3 - Footnote 3 B Total A & B Total
B.C. 4091 277 244 1852 2575 6666
Alta. 4375 1742 1287 1346 3417 7792
Sask. 1370 59 102 1209 700 2070
Man. 1648 174 134 1340 889 2537
Ont. 6516 2572 465 3479 2639 9155
Que. 12846 0 0 12846 10027 22873
N.B. 1047 61 29 957 1292 2339
N.S. 201 3 2 196 248 449
P.E.I. 144 0 0 144 78 222
N.L. 208 8 33 167 514 722
Y.T. 73 4 8 55 45 118
N.W.T 110 90 19 1 191 301
Nvt. 61 5 14 42 73 134
Canada 32690 4995 2337 23634 22688 55378
PercentageTable Figure 3 - Footnote 2 59% 15% 7% 72% 41% 100%
Table Figure 3 - Footnote 1

Specimens from NWT, YT, and Nvt are sent to reference laboratories in other provinces.

Return to Table Figure 3 - Footnote 1 referrer

Table Figure 3 - Footnote 2

Percentage of tests positive for sub-types of influenza A are a percentage of all influenza A detections.

Return to Table Figure 3 - Footnote 2 referrer

Table Figure 3 - Footnote 3

Unsubtyped: The specimen was typed as influenza A, but no result for subtyping was available.

Return to Table Figure 3 - Footnote 3 referrer

Table 1 - Cumulative number of positive influenza specimens by type, subtype and age group reported through case-based laboratory reporting, Canada, weeks 2019-35 to 2020-34
Age groups (years) Cumulative (August 25, 2019 to August 22, 2020)
Influenza A B Influenza A and B
A Total A(H1N1) A(H3N2) A (Un subtyped) Table 1 Footnote 1 Total # %
0-4 3798 441 213 3144 4050 7848 18%
5-19 2745 298 261 2186 5992 8737 21%
20-44 5227 961 331 3935 5584 10811 25%
45-64 5034 984 304 3746 1160 6194 15%
65+ 7543 1056 948 5539 1408 8951 21%
Total 24347 3740 2057 18550 18194 42541 100%
Table 1 Footnote 1

Unsubtyped: The specimen was typed as influenza A, but no result for subtyping was available.

Table 1 Return to footnote 1 referrer

Syndromic / Influenza-like Illness Surveillance

Healthcare Professionals Sentinel Syndromic Surveillance

In weeks 30 to 34, an average of 0.3% of visits to healthcare professionals were due to influenza-like illness (ILI) which continues to be lower than average compared to recent seasons. In these five weeks, the proportion of visits for ILI was the lowest observed for this period compared to the past 5 seasons (Figure 4). This trend should be interpreted with caution as there have been changes in healthcare seeking behavior of individuals and a decreasing number of sentinels reporting in recent weeks. Given the evolving Canadian situation with COVID-19, we will continue to monitor this indicator closely.

Figure 4 – Percentage of visits for ILI reported by sentinels by report week, Canada, weeks 2019-35 to 2020-34

Number of Sentinels Reporting in week 34: 84

Figure 4

The shaded area represents the maximum and minimum percentage of visits for ILI reported by week from seasons 2014-2015 to 2018-2019

Figure 4 - Text equivalent
Surveillance Week 2019-2020 Average Min Max
35 0.6% 0.6% 0.4% 0.9%
36 0.4% 0.6% 0.4% 0.9%
37 0.7% 0.7% 0.5% 1.0%
38 1.1% 0.7% 0.6% 1.0%
39 0.8% 0.9% 0.5% 1.2%
40 1.0% 1.2% 0.8% 1.7%
41 0.9% 1.7% 0.8% 2.8%
42 1.1% 1.6% 1.2% 2.1%
43 0.7% 1.2% 0.8% 1.7%
44 0.9% 1.2% 0.7% 1.7%
45 0.7% 1.2% 0.9% 1.5%
46 1.1% 1.4% 1.2% 1.8%
47 1.2% 1.6% 1.1% 2.2%
48 0.9% 1.5% 1.1% 2.2%
49 1.0% 1.7% 1.0% 2.8%
50 1.4% 1.5% 1.1% 1.7%
51 1.1% 1.9% 1.4% 2.7%
52 2.5% 2.0% 1.0% 3.1%
1 2.9% 3.4% 1.9% 5.4%
2 1.5% 3.4% 1.8% 5.7%
3 1.8% 2.3% 1.3% 3.7%
4 1.4% 2.0% 1.1% 2.9%
5 1.5% 2.1% 1.4% 3.1%
6 1.7% 2.4% 1.4% 4.0%
7 1.3% 2.4% 0.9% 3.5%
8 1.4% 2.3% 0.8% 3.4%
9 1.3% 2.3% 0.9% 3.1%
10 1.4% 2.0% 1.0% 2.8%
11 1.7% 1.9% 1.1% 2.8%
12 0.9% 1.6% 0.6% 2.6%
13 0.9% 1.6% 1.1% 2.6%
14 0.7% 1.7% 1.1% 3.0%
15 1.0% 1.3% 0.9% 1.9%
16 0.6% 1.2% 0.8% 1.7%
17 0.5% 1.2% 0.7% 1.7%
18 0.5% 1.3% 0.5% 2.0%
19 0.3% 0.9% 0.6% 1.3%
20 0.5% 1.1% 0.6% 1.5%
21 0.3% 0.9% 0.5% 1.3%
22 0.4% 0.7% 0.3% 1.0%
23 0.2% 0.8% 0.6% 1.0%
24 0.2% 0.7% 0.6% 1.0%
25 0.2% 0.6% 0.4% 0.8%
26 0.1% 0.8% 0.5% 1.4%
27 0.2% 0.6% 0.5% 0.7%
28 0.3% 0.7% 0.5% 1.3%
29 0.1% 0.9% 0.6% 1.7%
30 0.2% 0.6% 0.2% 0.9%
31 0.3% 0.4% 0.2% 0.6%
32 0.4% 0.8% 0.3% 1.2%
33 0.2% 0.7% 0.4% 1.3%
34 0.2% 0.7% 0.4% 1.5%

FluWatchers

In week 34, 9,320 participants reported to FluWatchers. During weeks 30 to 34, the proportion of participants reporting symptoms of cough and fever was low at an average of 0.10% (Figure 5). The percentage of participants reporting cough and fever are at the lowest levels ever observed. This decline was concurrent with public health measures to reduce the spread of COVID-19, which coincides with the abrupt end of the influenza season at the national level. Given the ongoing Canadian response to the COVID-19 pandemic, monitoring of this indicator will continue throughout the summer.  

Among the 21 participants who reported cough and fever in week 34, 38% (8) consulted a healthcare professional.

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

Figure 5 - Percentage of FluWatchers participants reporting cough and fever, Canada, weeks 2019-40 to 2020-34

Number of participants reporting in week 34 : 9,320

Figure 5. Text equivalent follows.
Figure 5 - Text equivalent
Surveillance Week % cough and fever
40 2.2%
41 1.8%
42 1.7%
43 2.2%
44 1.6%
45 1.4%
46 1.2%
47 1.5%
48 1.7%
49 2.2%
50 2.1%
51 2.6%
52 4.1%
1 4.3%
2 3.1%
3 3.3%
4 3.1%
5 3.4%
6 3.0%
7 2.7%
8 2.7%
9 2.4%
10 2.1%
11 2.5%
12 1.5%
13 0.9%
14 0.5%
15 0.3%
16 0.3%
17 0.2%
18 0.2%
19 0.3%
20 0.2%
21 0.1%
22 0.2%
23 0.1%
24 0.1%
25 0.1%
26 0.1%
27 0.1%
28 0.1%
29 0.1%
30 0.1%
31 0.1%
32 0.2%
33 0.2%
34 0.2%

Online Figure - Geographic distribution of FluWatchers participants reporting cough and fever, Canada, week 2020-34

Click on the map to access the link

map

Influenza Outbreak Surveillance

In weeks 30 to 34, no outbreaks of influenza or influenza-like illness were reported.

To date this season, a total of 958 laboratory-confirmed influenza outbreaks have been reported; 64% (615) in long-term care facilities, 25% (239) in facilities categorized as ‘other’, 9% (89) in acute care facilities, and 2% (15) in schools/daycares. Of the 910 outbreaks where influenza type was reported, 86% (787) were due to influenza A. Among the 324 outbreaks for which the influenza A subtype was reported, 54% were associated with A(H1N1) and 46% with A(H3N2). To date this season, 175 ILI outbreaks have also been reported; 98% (172) in schools/daycares and 2% (3) in facilities categorized as ‘other’.

Figure 6 - Number of new outbreaks of laboratory-confirmed influenza by report week, Canada, weeks 2019-35 to 2020-34

Number of provinces and territories reporting in week 34: 8 out of 13

Figure 6

Figure 6 - Text equivalent
Surveillance Week Acute Care Facilities Long Term Care Facilities Other Schools and Daycares Remote and/or Isolated Communities
35 0 0 0 0 0
36 0 0 0 0 0
37 0 0 0 0 0
38 0 1 0 0 0
39 0 1 0 0 0
40 0 2 0 0 0
41 0 2 1 0 0
42 1 0 0 0 0
43 0 0 1 0 0
44 0 0 1 0 0
45 0 2 4 0 0
46 1 4 0 0 0
47 0 2 1 1 0
48 1 6 2 2 0
49 2 10 1 1 0
50 4 10 4 1 0
51 4 17 11 0 0
52 4 48 15 0 0
1 17 85 40 0 0
2 12 92 36 0 0
3 10 52 7 1 0
4 5 50 19 3 0
5 5 23 9 0 0
6 8 17 26 4 0
7 1 32 13 1 0
8 4 34 6 1 0
9 2 31 8 0 0
10 1 20 3 0 0
11 1 34 13 0 0
12 1 15 8 0 0
13 3 9 2 0 0
14 0 6 2 0 0
15 0 3 0 0 0
16 0 0 2 0 0
17 0 0 0 0 0
18 0 0 0 0 0
19 0 1 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

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

To date this season, 2,485 influenza-associated hospitalizations were reported by participating provinces and territoriesFootnote 1.

308 ICU admissions and 120 deaths have been reported.

Figure 7 - Cumulative rates of influenza-associated hospitalization by age group and epidemiological week, Canada, participating provinces and territories Footnote 1 weeks 2019-35 to 2020-34

Number of provinces and territories reporting in week 34: 6 out of 9

Figure 7

Footnote 1

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.

Return to footnote 1 referrer

Figure 7 - Text equivalent
Surveillance Week 0-4 yrs 5-19 yrs 20-44 yrs 45-64 yrs 65+ yrs
35 0.0 0.0 0.0 0.0 0.0
36 0.0 0.0 0.0 0.0 0.2
37 0.0 0.0 0.0 0.1 0.2
38 0.0 0.0 0.0 0.1 0.4
39 0.2 0.0 0.0 0.1 0.6
40 0.2 0.0 0.0 0.1 0.8
41 0.4 0.2 0.1 0.2 1.1
42 0.8 0.2 0.1 0.2 1.3
43 1.0 0.2 0.2 0.3 1.6
44 1.5 0.2 0.2 0.5 2.1
45 1.9 0.4 0.4 0.8 2.8
46 1.9 0.4 0.6 1.1 3.3
47 3.1 0.6 0.8 1.5 4.6
48 5.0 1.1 1.0 1.6 5.7
49 7.1 1.9 1.3 2.0 7.5
50 11.1 3.0 1.8 2.3 10.2
51 14.3 3.7 2.5 3.5 13.6
52 18.7 5.8 3.7 4.5 19.3
1 27.7 6.5 4.8 6.6 28.1
2 33.8 7.6 6.0 8.4 34.5
3 38.8 8.4 7.0 10.0 40.4
4 43.7 9.6 8.2 11.8 45.4
5 52.3 10.8 9.4 13.5 50.9
6 57.3 11.9 10.5 15.0 55.7
7 59.4 12.8 11.2 16.3 59.5
8 62.1 13.8 11.9 17.4 63.4
9 65.1 14.5 12.4 18.5 67.0
10 68.0 15.3 13.0 19.8 71.3
11 71.4 15.7 13.4 20.8 74.8
12 72.4 15.9 13.7 21.4 76.7
13 73.3 16.0 13.8 21.7 77.5
14 73.3 16.0 13.8 21.7 77.7
15 73.3 16.0 13.8 21.7 77.7
16 73.3 16.0 13.8 21.7 77.7
17 73.3 16.0 13.8 21.7 77.7
18 73.3 16.0 13.8 21.7 77.7
19 73.3 16.0 13.8 21.7 77.7
20 73.3 16.0 13.8 21.7 77.7
21 73.3 16.0 13.8 21.7 77.7
22 73.3 16.0 13.8 21.7 77.7
23 73.3 16.0 13.8 21.7 77.7
24 75.4 16.3 14.2 22.8 79.0
25 75.4 16.3 14.2 22.8 79.0
26 75.4 16.3 14.2 22.8 79.0
27 75.8 16.3 14.2 22.8 78.9
28 75.8 16.3 14.2 22.8 78.9
29 75.8 16.3 14.2 22.8 78.9
30 75.8 16.3 14.2 22.8 78.9
31 75.8 16.3 14.2 22.8 78.9
32 75.8 16.3 14.2 22.8 78.9
33 75.8 16.3 14.2 22.8 78.9
34 75.8 16.3 14.2 22.8 78.9

Pediatric Influenza Hospitalizations and Deaths

In weeks 30 to 34, no pediatric (≤16 years of age) laboratory-confirmed influenza-associated hospitalizations were reported by the Immunization Monitoring Program Active (IMPACT) network (Figure 8). Since the end of March, the weekly number of reported cases has been at the lowest level observed during this period over the past 5 seasons.

To date this season (weeks 35 to 34):

Figure 8 - Number of pediatric (≤16 years of age) hospitalizations reported by the IMPACT network, by week, Canada, weeks 2019-35 to 2020-34

Figure 8

The shaded area represents the maximum and minimum number of cases reported by week from seasons 2014-15 to 2018-24

Figure 8 - Text equivalent
Surveillance week 2019-2020 Average Min Max
35 0 0 0 1
36 2 0 0 1
37 0 1 0 2
38 0 1 0 2
39 1 1 0 3
40 0 1 0 2
41 2 1 0 3
42 2 2 0 5
43 1 5 2 12
44 2 5 1 15
45 3 10 2 37
46 6 13 1 41
47 6 13 2 36
48 27 18 2 40
49 23 22 3 47
50 38 29 4 50
51 58 41 5 84
52 102 54 14 89
1 105 55 21 94
2 100 40 12 63
3 79 44 28 64
4 90 53 34 93
5 116 47 25 70
6 115 49 15 79
7 63 59 17 120
8 83 63 25 139
9 61 58 13 153
10 47 55 17 135
11 47 51 18 118
12 24 39 13 89
13 4 32 14 67
14 2 29 12 56
15 0 26 14 56
16 0 22 9 41
17 0 20 8 37
18 1 16 9 28
19 0 11 5 19
20 1 11 1 19
21 0 7 4 11
22 0 6 1 8
23 0 3 1 6
24 1 3 0 7
25 0 2 0 5
26 0 1 0 3
27 0 1 0 2
28 0 1 0 2
29 1 1 0 3
30 0 1 0 2
31 0 0 0 0
32 0 0 0 0
33 0 0 0 2
34 0 1 0 2
Figure 9 - Cumulative number of pediatric hospitalizations (≤16 years of age) with influenza by age-group reported by the IMPACT network, Canada, weeks 2019-35 to 2020-34

Figure 9

Figure 9 - Text Description
Age Group Total
0-5 mo 142
6-23 mo 318
2-4 yr 338
5-9 yr 270
10-16 yr 154

Adult Influenza Hospitalizations and Deaths

Surveillance of laboratory-confirmed influenza-associated adult (≥16 years of age) hospitalizations by the Canadian Immunization Research Network (CIRN) Serious Outcomes Surveillance (SOS) network began on November 1st and ended  May 9th for the 2019-20 season.

To date this season, 802 hospitalizations, 89 intensive care unit admissions, and 44 deaths have been reported (Figure 10).

Figure 10 - Number of adult hospitalizations (≥16 years of age) with influenza reported by the CIRN-SOS network, by week, Canada, weeks 2019-45 to 2020-19

Figure 10

Figure 10 - Text Description
Surveillance Week Number of Hospitalizations
35 No data
36 No data
37 No data
38 No data
39 No data
40 No data
41 No data
42 No data
43 No data
44 No data
45 No data
46 2
47 4
48 9
49 12
50 13
51 38
52 88
1 95
2 67
3 57
4 49
5 59
6 65
7 51
8 52
9 56
10 30
11 19
12 10
13 12
14 1
15 2
16 1
17 1
18 2
19 1
20 0
21 0
22 0
23 0
24 0
25 0
26 0
27 0
28 0
29 0
30 0
31 0
32 0
33 0
34 0
Figure 11 - Cumulative numbers of adult hospitalizations (≥16 years of age) with influenza by age-group reported by the CIRN-SOS network, Canada, weeks 2019-45 to 2020-19

Figure 11

Figure 11 - Text Description
Age Group Total hospitalizations
16-34 yr 82
35-49 yr 64
50-64 yr 147
65-79 yr 262
80+ yr 247

Influenza Strain Characterizations

From September 1, 2019 to July 23, 2020, the National Microbiology Laboratory (NML) has characterized 2,021 influenza viruses (760 A(H1N1), 368 A(H3N2) and 893 influenza B) that were received from Canadian laboratories.

Influenza A(H3N2)

Over recent years, circulating strains of A(H3N2) have evolved, and are increasingly difficult to characterize by hemagglutination inhibition (HI) assay. Genetic characterization is established by sequencing the hemagglutinin (HA) gene of the influenza viruses to compare their genetic properties.

Antigenic Characterization:

Among the 109 influenza A(H3N2) viruses antigenically characterized to date, the majority (79%) showed reduced titer by HI assay to A Kansas/14/2017 using antiserum raised against egg-propagated A Kansas/14/2017. Twenty-three viruses were characterized as A Kansas/14/2017-like (Figure 12a).

Genetic Characterization:

Nearly all (96%) of the 368 A(H3N2) viruses genetically characterized this season belonged to genetic group 3C.2a1b based on sequence analysis of the HA gene. Fifteen viruses belonged to the genetic group 3C.3a (Figure 13).

Group 3C.2a1b viruses analysed represent:

A/Kansas/14/2017 belongs to genetic group 3C.3a and is the influenza A(H3N2) component of the 2019-20 Northern Hemisphere influenza vaccine.

Influenza A(H1N1)

Among the 760 A(H1N1) viruses characterized to date, 50% were antigenically similar to A/Brisbane/02/2018 by HI testing using antiserum raised against egg-propagated A/Brisbane/02/2018 (Figure 12b).

A/Brisbane/02/2018 is the influenza A(H1N1) component of the 2019-20 Northern Hemisphere influenza vaccine.

Influenza B

Antigenic Characterization:

Among the 184 influenza B viruses antigenically characterized this season, the vast majority (181) belonged to the B/Victoria lineage. Three viruses were antigenically characterized as similar to B/Phuket/3073/2013 (B/Yamagata lineage).

The majority (90%, 162) of B/Victoria lineage viruses showed reduced titer by HI assay to B/Colorado/06/2017 using antiserum raised against cell culture-propagated B/Colorado/06/2017 (Figure 12c).

Sequence analysis of 161 B/Victoria lineage viruses with reduced titre to B/Colorado/06/2017 showed that 100% had a three amino acid deletion (162-164) in the HA gene and belong to the genetic subclade V1A.3 (3Del). Sequencing is pending for the remaining viruses.

Genetic Characterization:

Genetic characterization was also performed on 481 B/Victoria lineage viruses. All of these viruses had a three amino acid deletion (162-164) in the HA gene and belong to the genetic subclade V1A.3 (3Del).

To date, 100% (709) of influenza B/Victoria viruses genetically characterized belong to the genetic subclade V1A.3 (3Del) (Fig 13b). Viruses in this genetic subclade are antigenically distinct from the vaccine strain B/Colorado/06/2017, which belongs to genetic subclade V1A.1 (2Del).

The recommended influenza B components for the 2019-20 Northern Hemisphere influenza vaccine are B/Colorado/06/2017 (Victoria lineage) and B/Phuket/3073/2013 (Yamagata lineage). B/Phuket/3073/2013 is included in the quadrivalent influenza vaccine. The vaccine strain B/Colorado/06/2017 belongs to genetic subclade V1A.1.

Figure 12 - Distribution of antigenic phenotypes among characterized influenza viruses, Canada, September 1, 2019 to July 23, 2020

Figure 12

Figure 12 - Text Description
A) Antigenic phenotypes among influenza A(H3N2) viruses
Number of viruses characterized: 109
Antigenic phenotype of A(H3N2) virus Number of viruses Percentage
A/Kansas/14/2017-like 23 21%
Reduced titer to A/Kansas/14/2017 86 79%
B) Antigenic phenotypes among influenza A(H1N1) viruses
Number of viruses characterized: 760
Antigenic phenotype of A(H1N1) virus Number of viruses Percentage
A/Brisbane/02/2018-like 378 50%
Reduced titer to A/Brisbane/02/2018 382 50%
C) Antigenic phenotypes among influenza B viruses
Number of viruses characterized: 184
Antigenic phenotype of influenza B virus Number of viruses Percentage
B/Colorado/06/2017-like 19 10%
Reduced titer to B/Colorado/06/2017 162 88%
B/Phuket/3073/2013-like 3 2%
Figure 13 - Distribution of genetic clades among characterized influenza viruses, Canada, September 1, 2019 to July 23, 2020

Figure 13

Figure 13 - Text Description
A) Distribution of genetic clades among characterized A(H3N2) viruses
Number of viruses sequenced: 368
Genetic Clade of A(H3N2) virus Number of viruses Percentage
Subclade 3C.2a1b 353 96%
Clade 3C.3a 15 4%
B) Distribution of genetic clades among characterized influenza B/Victoria viruses
Number of viruses sequenced: 871
Genetic Clade of influenza B/Victoria virus Number of viruses Percentage
Subclade V1A.3 (3Del) 871 100%
Subclade V1A.1 (2Del) 0 0%

Antiviral Resistance

The National Microbiology Laboratory (NML) also tests influenza viruses received from Canadian laboratories for antiviral resistance. From September 1, 2019 to April 9, 2020, the following results were reported:

Oseltamivir:

733 influenza viruses (164 A(H3N2), 283 A(H1N1) and 286 B) were tested for resistance to oseltamivir:

Zanamivir:

733 influenza viruses (164 A(H3N2), 283 A(H1N1) and 286 B) were tested for resistance to zanamivir:

Amantadine:

High levels of resistance to amantadine persist among influenza A(H1N1) and influenza A(H3N2) viruses. All viruses tested this season were resistant.

Vaccine Monitoring

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

Vaccine Coverage

The Seasonal Influenza Immunization 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. Vaccine coverage is measured as the percentage of people who received the influenza vaccine in a specific influenza season.

In the 2019-20 influenza season, coverage was similar to the 2018-19 season, at:

Table 2 – Influenza vaccine coverage among adults (n=3,026)Table 2 - Footnote * by age group genderTable 2 - Footnote and medical conditionsTable 2 - Footnote , Seasonal Influenza Vaccination Coverage Survey, Canada, September 2019 – February 2020
Age group (years) All Male Female
N Vaccine Coverage %
(95% CI)
N Vaccine Coverage %
(95% CI)
N Vaccine Coverage %
(95% CI)
All adults (≥18) 3023 41.8 (39.7-43.9) 1320 37.2 (34.1-40.2) 1691 46.1 (43.2-49.0)
18-64 2234 34.1 (31.8-36.5) 1005 29.8 (26.5-33.1) 1218 38.4 (35.1-41.7)
with chronic diseases 668 43.6 (39.0-48.1) 268 38.3 (31.5-45.2) 397 47.9 (41.7-54.0)
without chronic diseases 1558 30.0 (27.3-32.7) 732 26.7 (22.9-30.5) 818 33.5 (29.6-37.3)
≥65 789 70.3 (66.7-73.8) 315 67.2 (61.5-72.9) 473 72.7 (68.3-77.1)
CI: 95% confidence interval
Footnote *

3 people did not recall whether they had received the influenza vaccine and were excluded from coverage estimates.

Return to table 2 footnote * referrer

Footnote ‡

4 people did not disclose their gender and 8 people did not identify themselves as male nor female. They were excluded from stratified analysis.

Return to table 2 footnote referrer

Footnote †

8 people who were 18-64 years old did not disclose whether they had any chronic medical conditions (CMC) and were excluded from stratified analysis.

Return to table 2 footnote referrer

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, 2019 and February 1, 2020, vaccine effectiveness (VE) was estimated to be 58% for any influenza, 44% for influenza A(H1N1), 62% for influenza A(H3N2), and 69% for influenza B. Substantial protection was observed among children 1 to 19 years of age against both influenza A and B. A good level of protection was also observed among working age adults (20-64 yrs) across all influenza types (Table 2). VE among adults 65 years and older, although imprecise due to small numbers, was lower at 18% (95% CI -59 to 58). The SPSN interim estimates are published and available online.

More information on the network and past VE findings can be viewed on the SPSN website.

Updated influenza vaccine effectiveness estimates will be published at the end of the 2019/2020 influenza season. At that time, sufficient data will likely be available to estimate VE by age-group, including adults 65 years and older with greater precision, as well as for influenza A subtypes.

Table 3 - Vaccine effectiveness estimates against medically-attended influenza illness, SPSN, November 1, 2019, to February 1, 2020
  All ages 1-19 years 20-64 years
VE(%) (CI)Table 3 - Footnote * N VE(%) (CI)Table 3 - Footnote * VE(%) (CI)Table 3 - Footnote *
All Influenza 58 (47, 66) 2808 74 (59, 84) 55 (41, 66)
Influenza A 49 (34, 60) 2128 70 (44, 84) 45 (25, 59)
Influenza A(H1N1) 44 (26, 58) 1948 - -
Influenza A(H3N2) 62 (37, 77) 1561 - -
Influenza B 69 (57, 77) 2080 77 (59, 87) 68 (51, 79)
Footnote *

adjusted for age group, province, specimen collection interval and calendar time

Return to table 2 footnote * referrer

Page details

Date modified: