FluWatch report: March 22 to 28, 2020 (week 13)

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Organization: Public Health Agency of Canada

Date published: 2020-04-03

Related Topics

Overall Summary

  • The percentage of tests positive for influenza fell below 5% this week. This suggests that Canada is nearing the end of the 2019-2020 influenza season at the national level.
  • All indicators of influenza activity decreased compared to the previous week.
  • Laboratory detections and syndromic indicators may be influenced by the COVID-19 pandemic. These data should be interpreted with caution.
  • The 2019-2020 Seasonal Influenza Immunization Coverage Survey showed that coverage was low among adults aged 18-64 years (34%) and highest among seniors aged 65 years and older (70%).
  • The highest cumulative hospitalization rates are among children under 5 years of age and adults 65 years of age and older. Hospitalizations among adults are predominantly due to influenza A, while those among children are due to a mix of influenza A and B.

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

During week 13, influenza activity was reported in 33 regions across Canada and 4 regions reported no influenza activity. Among the regions reporting influenza activity, 65% reported sporadic activity and 24 % reported localized activity (Figure 1).

Figure 1 - Map of influenza/ILI activity by province and territory, Canada, week 2020-13

Number of Regions Reporting in week 13: 37 out of 53

Figure 1. Text equivalent follows.

Figure 1 - Text equivalent
Province Influenza Surveillance Region Activity Level
N.L. Eastern No Data
N.L. Labrador-Grenfell Sporadic
N.L. Central No Data
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 Localized
N.B. Region 2 Sporadic
N.B. Region 3 Sporadic
N.B. Region 4 No Activity
N.B. Region 5 Sporadic
N.B. Region 6 Localized
N.B. Region 7 Localized
Que. Nord-est Sporadic
Que. Québec et Chaudieres-Appalaches No Activity
Que. Centre-du-Québec Localized
Que. Montréal et Laval Sporadic
Que. Ouest-du-Québec Sporadic
Que. Montérégie No Activity
Ont. Central East Localized
Ont. Central West Localized
Ont. Eastern Localized
Ont. North East Localized
Ont. North West Sporadic
Ont. South West Localized
Ont. Toronto No Data
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 No Data
Sask. Central No Data
Sask. South No Data
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 Sporadic
B.C. Fraser Sporadic
B.C. Vancouver Coastal Sporadic
B.C. Vancouver Island Sporadic
B.C. Northern Sporadic
Y.T. Yukon Sporadic
N.W.T. North Sporadic
N.W.T. South Sporadic
Nvt. Qikiqtaaluk Sporadic
Nvt. Kivalliq No Activity
Nvt. Kitimeot Sporadic

Laboratory-Confirmed Influenza Detections

In week 13, the percentage of laboratory tests positive for influenza continued to decrease sharply to 2.5%. The percentage of positive tests crossed the seasonal threshold of 5%, suggesting that the end of the influenza season at the national level may have occurred last week.

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

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

To date this season (weeks 35 to 13), all influenza types and subtypes have circulated. Among the 55,033 laboratory detections of influenza reported:

Detailed information on age and type/subtype has been received for 42,355 laboratory-confirmed influenza cases (Table 1). To date this season (weeks 35 to 13):

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 2020-13

Number of Laboratories Reporting in Week 13: 33 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 1773 81 399 1152 13.6 6.5
11 1552 70 354 1016 9.8 4.3
12 830 38 152 594 4.8 2.5
13 179 17 33 265 1.3 1.3

Figure 3 - Distribution of positive influenza specimens by type/subtype and province/territory, Canada, weeks 2019-35 to 2020-13

Figure 3. Text equivalent follows.
Figure 3 - Text equivalent
ProvincesTable Figure 3 - Footnote 1 Cumulative (August 25, 2019 to March 28, 2020)
A Total A(H1N1) A(H3N2) A(UnS)Table Figure 3 - Footnote 3 B Total A & B Total
B.C. 4072 276 243 1846 2552 6624
Alta. 4352 1721 1285 1346 3403 7755
Sask. 1370 59 102 1209 700 2070
Man. 1637 174 134 1329 883 2520
Ont. 6468 2563 459 3446 2554 9022
Que. 12827 0 0 12827 10025 22852
N.B. 1045 60 29 956 1292 2337
N.S. 195 3 2 190 238 433
P.E.I. 144 0 0 144 78 222
N.L. 200 8 33 159 491 691
Y.T. 70 4 8 55 35 105
N.W.T 107 87 19 1 186 293
Nvt. 60 5 14 41 49 109
Canada 32547 4960 2328 23549 22486 55033
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 2020-13
Age groups (years) Cumulative (August 25, 2019 to March 28, 2020)
Influenza A B Influenza A and B
A Total A(H1N1) A(H3N2) A (Un subtyped) Table 1 Footnote 1 Total # %
0-4 3797 441 213 3143 4037 7834 18%
5-19 2741 297 261 2183 5983 8724 21%
20-44 5216 963 330 3923 5539 10755 25%
45-64 5012 978 303 3731 1143 6155 15%
65+ 7503 1050 941 5512 1384 8887 21%
Total 24269 3729 2048 18492 18086 42355 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 week 13, 1.1% of visits to healthcare professionals were due to influenza-like illness (ILI) which is a slight decrease from the previous week and around average for this time of year (Figure 4). This trend should be interpreted with caution as there continues to be a decreasing number of sentinels reporting. 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 2020-13

Number of Sentinels Reporting in week 13: 60

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 1.4% 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 1.4% 1.6% 0.6% 2.6%
13 1.1% 1.6% 1.1% 2.6%

FluWatchers

In week 13, 3,124 participants reported to FluWatchers, of which 0.9% (27) reported symptoms of cough and fever (Figure 5).The percentage of participants reporting cough and fever continue to decrease and are at the lowest levels ever observed. This may be due to social distancing measures implemented in recent weeks. Given the evolving Canadian situation with COVID-19, we will continue to monitor this indicator closely.

Among the 27 participants who reported cough and fever:

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 2020-13

Number of participants reporting in week 13: 3,124

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%

Online Figure - Geographic distribution of FluWatchers participants reporting cough and fever, Canada, week 2020-13

Click on the map to access the link

map

Influenza Outbreak Surveillance

In week 13, a total of 5 outbreaks were reported: 3 in long term care facilities and 2 in acute care facilities (Figure 6).

To date this season, a total of 903 laboratory-confirmed influenza outbreaks have been reported; 65% (583) in long-term care facilities, 25% (221) in facilities categorized as ‘other’, 9% (84) in acute care facilities, and 2% (15) in schools/daycares. Of the 855 outbreaks where influenza type was reported, 88% (750) were due to influenza A. Among the 307 outbreaks for which the influenza A subtype was reported, 53% were associated with A(H1N1) and 47% with A(H3N2). To date this season, 175 ILI outbreaks have also been reported; 98% (171) in schools/daycares and 2% (4) in facilities categorized as ‘other’.

Figure 6 - Number of new outbreaks of laboratory-confirmed influenza by report week, Canada, weeks 2019-35 to 2020-13

Number of provinces and territories reporting in week 13: 10 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 16 11 0 0
52 4 48 15 0 0
1 17 86 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 25 4 0
7 1 31 12 1 0
8 4 32 6 1 0
9 2 32 7 0 0
10 1 19 3 0 0
11 0 31 12 0 0
12 0 11 4 0 0
13 2 3 0 0 0

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

To date this season, 2,333 influenza-associated hospitalizations were reported by participating provinces and territories Footnote 1.

285 ICU admissions and 102 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 2020-13

Number of provinces and territories reporting in week 13: 4 out of 9

Figure 7

Footnote ‡

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 52.5 10.7 9.4 13.5 50.9
6 57.5 11.8 10.5 15.0 55.7
7 59.6 12.8 11.2 16.3 59.5
8 62.6 13.7 11.9 17.3 63.4
9 65.3 14.4 12.3 18.4 66.8
10 68.2 15.2 12.9 19.5 71.0
11 70.7 15.4 13.3 20.2 73.7
12 71.2 15.6 13.5 20.5 74.8
13 73.3 16.0 13.8 21.0 76.7

Pediatric Influenza Hospitalizations and Deaths

In week 13, four pediatric (≤16 years of age) laboratory-confirmed influenza-associated hospitalizations were reported by the Immunization Monitoring Program Active (IMPACT) network (Figure 8). Since the beginning of March, the weekly number of reported cases have dropped below the 5-year weekly average.

To date this season (weeks 35 to 13):

Figure 8 - Number of pediatric (≤16 years of age) hospitalizations reported by the IMPACT network, by week, Canada, weeks 2019-35 to 2020-13

Figure 8

The shaded area represents the maximum and minimum number of cases reported by week from seasons 2014-15 to 2018-19

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 26 18 2 40
49 23 22 3 47
50 38 29 4 50
51 57 41 5 84
52 104 54 14 89
1 105 55 21 94
2 101 40 12 63
3 81 44 28 64
4 91 53 34 93
5 111 47 25 70
6 111 49 15 79
7 66 59 17 120
8 85 63 25 139
9 57 58 13 153
10 50 55 17 135
11 46 51 18 118
12 26 39 13 89
13 4 32 14 67
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 2020-13

Figure 9

Figure 9 - Text Description
Age Group Total
0-5 mo 143
6-23 mo 316
2-4 yr 334
5-9 yr 264
10-16 yr 150

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  for the 2019-20 season.

To date this season, 787 hospitalizations, 87 intensive care unit admissions, and 42 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 2020-13

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 87
1 93
2 67
3 57
4 48
5 59
6 64
7 51
8 52
9 56
10 30
11 19
12 11
13 10
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 2020-13

Figure 11

Figure 11 - Text Description
Age Group Total hospitalizations
16-34 yr 81
35-49 yr 64
50-64 yr 145
65-79 yr 254
80+ yr 243

Influenza Strain Characterizations

From September 1, 2019 to March 19, 2020, the National Microbiology Laboratory (NML) has characterized 1,224 influenza viruses (474 A(H1N1), 177 A(H3N2) and 573 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 55 influenza A(H3N2) viruses antigenically characterized to date, the majority (80%) showed reduced titer by HI assay to A Kansas/14/2017 using antiserum raised against egg-propagated A Kansas/14/2017. Eleven viruses were characterized as A Kansas/14/2017-like (Figure 12a).

Genetic Characterization:

Nearly all (98%) of the 160 A(H3N2) viruses genetically characterized this season belonged to genetic group 3C.2a1b based on sequence analysis of the HA gene. Three 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 474 A(H1N1) viruses characterized to date, 53% were antigenically similar to A/Brisbane/02/2018 by HI testing using antiserum raised against egg-propagated A/Brisbane/02/2018 (Figure 12 b).

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

Influenza B

Antigenic Characterization:

Among the 182 influenza B viruses antigenically characterized this season, the vast majority (180) belonged to the B/Victoria lineage. Two viruses were antigenically characterized as similar to B/Phuket/3073/2013 (B/Yamagata lineage).

The majority (89%, 161) 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 150 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 391 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% (541) 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 March 19, 2020

Figure 12

Figure 12 - Text Description
A) Antigenic phenotypes among influenza A(H3N2) viruses
Number of viruses characterized: 55
Antigenic phenotype of A(H3N2) virus Number of viruses Percentage
A/Kansas/14/2017-like 11 20%
Reduced titer to A/Kansas/14/2017 44 80%
B) Antigenic phenotypes among influenza A(H1N1) viruses
Number of viruses characterized: 474
Antigenic phenotype of A(H1N1) virus Number of viruses Percentage
A/Brisbane/02/2018-like 251 53%
Reduced titer to A/Brisbane/02/2018 223 47%
C) Antigenic phenotypes among influenza B viruses
Number of viruses characterized: 182
Antigenic phenotype of influenza B virus Number of viruses Percentage
B/Colorado/06/2017-like 19 10%
Reduced titer to B/Colorado/06/2017 161 88%
B/Phuket/3073/2013-like 2 1%
Figure 13 - Distribution of genetic clades among characterized influenza viruses, Canada, September 1, 2019 to March 19, 2020

Figure 13

Figure 13 - Text Description
A) Distribution of genetic clades among characterized A(H3N2) viruses
Number of viruses sequenced: 160
Genetic Clade of A(H3N2) virus Number of viruses Percentage
Subclade 3C.2a1b 157 98%
Clade 3C.3a 3 2%
B) Distribution of genetic clades among characterized influenza B/Victoria viruses
Number of viruses sequenced: 541
Genetic Clade of influenza B/Victoria virus Number of viruses Percentage
Subclade V1A.3 (3Del) 541 100%
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 March 19, 2020, the following results were reported:

Oseltamivir:

669 influenza viruses (155 A(H3N2), 251 A(H1N1) and 263 B) were tested for resistance to oseltamivir:

Zanamivir:

669 influenza viruses (155 A(H3N2), 251 A(H1N1) and 263 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

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