FluWatch annual report: 2018-19 influenza season

Overall Summary

  • During the influenza season, the FluWatch report is based on weekly data. This report is a summary of all of  the data received for the 2018-19 influenza season and a comparison of these data to the previous five seasons.
  • The 2018-19 influenza season in Canada was longer than the previous five seasons and was characterized by two waves of influenza A activity and very little influenza B circulation. The national season started in week 43 (October 21-27, 2018), peaked in week 52 (December 23-29, 2018) and ended in week 21 (May 19-25, 2019).
  • A(H1N1) was predominant in the earlier part of the season (October to February) followed by a smaller wave of A(H3N2) circulation (March to April). Overall, A(H1N1) was the predominant strain nationally this season.
  • Two waves of activity were observed in the number of reported outbreaks. The predominant subtype for typed outbreaks was A(H1N1) in the early part of the season (October to January), and A(H3N2)  in the latter part of the season (Feburary onward).
  • The annual seasonal hospitalization rate was above average compared to the previous five seasons. Adults 65 years of age and older had the highest overall hospitalization rate; however, the highest cumulative hospitalization rate shifted during the season from children 0-4 years of age (November to March)  to adults 65 years of age and older (March onward), likely due to the second wave of A(H3N2).
  • Overall, influenza vaccine coverage in the 2018-19 season (42%) was significantly higher than in the previous two seasons. Coverage was estimated at 34% for adults aged 18 to 64 years and 70% among seniors.
  • Vaccine effectiveness studies in both the outpatient setting and adult inpatient setting observed good protection against A(H1N1) and little to no protection against A(H3N2) viruses relative to what is expected for influenza vaccine effectiveness.

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Organization: Public Health Agency of Canada

Published: 2019-XX-XX

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

Data on the geographic spread of influenza and influenza-like illness (ILI) are provided by all provinces and territories. All provinces and territories reported activity level data for each week of the 2018-19 influenza season.

Figure 1 – Number of regions reporting widespread and localized influenza activity, Canada, weeks 2018-35 to 2019-34

Figure 1

Text description
Surveillance Week Localized Widespread
35 0 0
36 0 0
37 0 0
38 1 0
39 0 0
40 3 0
41 0 0
42 3 0
43 6 0
44 3 0
45 4 0
46 6 0
47 6 1
48 11 0
49 8 0
50 13 1
51 13 0
52 11 3
1 20 3
2 23 2
3 27 2
4 20 3
5 19 0
6 20 0
7 18 1
8 20 3
9 20 1
10 20 2
11 21 2
12 21 1
13 27 2
14 26 1
15 25 0
16 19 1
17 17 0
18 22 0
19 10 0
20 11 0
21 6 0
22 3 0
23 5 0
24 1 0
25 3 0
26 1 0
27 1 0
28 0 0
29 1 0
30 1 0
31 0 0
32 1 0
33 0 0
34 0 0

Laboratory-Confirmed Influenza Detections

Data on laboratory-confirmed influenza detections are provided by 32 provincial, regional and some hospital laboratories. On average 99.6% of labs reported each week. During the 2018-19 season a total of 48,818 influenza detections were reported. Based on the seasonal thresholds for start and end of season (i.e. when the percentage of tests positive for influenza crossed 5%), the national influenza season started in week 43, peaked in week 52 and ended in week 21 (Figure 2).

Detailed information on age and influenza type/subtype was received for 39,192 of laboratory-confirmed influenza cases. Among influenza A detections where subtype was identified (13,718), subtype distribution varied by age-group (Figure 4). A(H1N1) was the predominant subtype in all age groups except those 65 years of age and older, among whom A(H3N2) was the predominant subtype (66%). Children less than five years of age had the highest proportion of A(H1N1) among subtyped influenza A detections (86%).

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 positive tests, by type, subtype and report week, Canada, weeks 2018-35 to 2019-34

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.

Data for week 14 excludes subtyping results from one jurisdiction due to batch reporting of subtype information. The results for week 14 should be interpreted with caution.

Text description
Surveillance Week A(Unsubtyped) A(H3N2) A(H1N1) Influenza B
35 3 2 7 0
36 4 7 4 0
37 3 2 3 1
38 6 3 2 3
39 11 5 1 3
40 16 7 29 3
41 27 6 21 3
42 40 19 55 2
43 83 23 128 4
44 169 13 214 6
45 244 18 295 15
46 346 10 404 9
47 449 17 507 8
48 679 29 632 10
49 851 35 785 16
50 1368 35 828 14
51 1890 54 953 21
52 2292 55 903 26
1 2387 58 893 31
2 1985 93 1061 43
3 1613 101 585 40
4 1483 93 532 48
5 1449 112 433 43
6 1234 118 315 42
7 1116 128 244 33
8 1066 236 216 40
9 1172 285 213 64
10 1085 335 268 71
11 990 357 197 90
12 959 380 155 131
13 939 387 128 167
14 1091 292 41 169
15 756 514 121 157
16 614 277 42 175
17 448 244 55 194
18 265 160 29 148
19 266 154 33 151
20 137 163 27 136
21 89 79 8 122
22 43 53 17 75
23 33 42 8 60
24 39 44 5 48
25 29 41 4 31
26 23 30 0 27
27 15 23 3 12
28 10 18 2 11
29 8 17 1 9
30 5 13 1 6
31 3 15 6 7
32 8 13 2 0
33 9 4 0 5
34 8 12 7 6

Figure 3 – Cumulative numbers of positive influenza specimens by type/subtype and province/territory, Canada, weeks 2018-35 to 2019-34

Figure 3

Text description
Provinces and TerritoriesFigure 3 Footnote 1 Cumulative (August 26, 2018 to August 24, 2019)
Influenza A B A & B
A Total A(H1N1)pdm09 A(H3N2) A(UnS)Figure 3 Footnote 3 B Total Total
B.C. 6480 3165 1689 1626 244 6724
Alta. 7266 3649 1392 2225 370 7636
Sask. 2458 1389 142 927 109 2567
Man. 1194 335 131 728 77 1271
Ont. 6422 2112 1733 2577 311 6733
Que. 17167 0 0 17167 988 18155
N.B. 2884 246 39 2599 366 3250
N.S. 786 0 0 786 22 808
P.E.I 279 221 56 2 2 281
N.L. 1036 1 0 1035 13 1049
Y.T. 140 66 35 39 0 140
N.W.T 181 175 6 0 3 184
Nvt. 20 20 0 0 0 20
Canada 46313 11379 5223 29711 2505 48818
PercentageFigure 3 Footnote 2 95% 25% 11% 64% 5% 100%
Figure 3 Footnote 1

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

Figure 3 Return to footnote 1 referrer

Figure 3 Footnote 2

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

Figure 3 Return to footnote 2 referrer

Figure 3 Footnote 3

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

Figure 3 Return to footnote 3 referrer

Figure 4 – Proportion of positive influenza A specimens by subtype and age-group reported through case-based laboratory reporting, Canada, weeks 2018-35 to 2019-34

Figure 4

Text description
Age group A(H1N1) A(H3N2)
0-4 yr 86% 14%
5-19 yr 73% 27%
20-44 yr 75% 25%
45-64 yr 73% 27%
65+ yr 34% 66%

Syndromic / Influenza-like Illness Surveillance

Healthcare Practitioners Sentinel Syndromic Surveillance

On average, during the 2018-19 season, 106 healthcare practitioners across the country participated in influenza-like illness (ILI) surveillance for the FluWatch program. Each week these sentinel healthcare practioners report the proportion of patients in their practice who had ILI.

Figure 5 – Percentage of visits for ILI reported by sentinels by report week, Canada, weeks 2018-35 to 2019-34

Figure 5

The shaded area represents the maximum and minimum percentage of visits for ILI reported by week from seasons 2013-2014 to 2017-2018

Text description
Surveillance Week 2018-19 Average  Min Max
35 0,6% 0,8% 0,5% 1,2%
36 0,7% 0,8% 0,7% 1,0%
37 0,6% 0,9% 0,7% 1,0%
38 0,5% 1,1% 1,0% 1,4%
39 1,7% 1,1% 0,9% 1,4%
40 0,8% 1,3% 0,9% 1,6%
41 1,3% 1,4% 0,9% 2,4%
42 1,0% 1,4% 1,0% 1,9%
43 0,9% 1,3% 1,0% 1,5%
44 0,9% 1,3% 0,9% 1,6%
45 1,3% 1,3% 1,2% 1,5%
46 1,3% 1,6% 1,0% 2,0%
47 1,3% 1,5% 1,1% 1,9%
48 1,4% 1,6% 0,8% 2,1%
49 1,6% 1,5% 1,0% 2,5%
50 1,4% 2,3% 1,3% 3,7%
51 1,0% 2,5% 1,6% 4,1%
52 3,2% 4,5% 1,7% 7,1%
1 2,8% 3,7% 1,7% 5,2%
2 1,8% 3,0% 1,1% 4,5%
3 1,1% 2,5% 1,3% 3,6%
4 1,4% 2,4% 1,7% 3,5%
5 1,4% 2,7% 2,0% 4,4%
6 0,9% 2,7% 2,1% 3,3%
7 0,8% 2,4% 1,7% 3,0%
8 0,9% 2,3% 1,9% 2,7%
9 1,0% 2,2% 1,8% 2,7%
10 1,1% 2,1% 1,8% 2,7%
11 0,6% 2,1% 1,7% 2,7%
12 1,1% 1,8% 1,1% 2,7%
13 1,1% 1,7% 1,2% 2,6%
14 1,0% 1,8% 1,3% 2,4%
15 0,8% 1,6% 0,9% 1,9%
16 0,7% 1,5% 1,0% 1,9%
17 0,5% 1,5% 0,9% 2,2%
18 0,6% 1,2% 0,8% 1,6%
19 0,6% 1,3% 1,0% 1,7%
20 0,5% 1,2% 0,9% 1,4%
21 0,6% 0,9% 0,3% 1,3%
22 0,6% 0,8% 0,6% 1,0%
23 0,6% 0,9% 0,6% 1,2%
24 0,6% 0,7% 0,4% 1,0%
25 0,5% 1,2% 0,5% 1,6%
26 0,6% 0,8% 0,4% 1,4%
27 0,6% 0,8% 0,4% 1,5%
28 0,7% 1,0% 0,6% 1,9%
29 0,2% 0,8% 0,5% 1,1%
30 0,2% 0,5% 0,3% 0,7%
31 0,3% 0,9% 0,3% 1,4%
32 0,4% 1,0% 0,6% 1,6%
33 0,5% 1,2% 0,4% 2,1%
34 0,4% 0,7% 0,5% 0,9%

Participatory Syndromic Surveillance

FluWatchers are Canadians who report via a weekly online questionnaire if they have had symptoms of ILI in the preceding week. FluWatchers surveillance for the 2018-19 started in week 40 (October) and ended in week 18 (May). A total of 3,205 participants reported at least once this season, resulting in 64,728 completed questionnaires.

Figure 6 – Percentage of FluWatchers participants reporting fever and cough, Canada, weeks 2018-40 to 2019-18

Figure 6

Text description
Surveillance Week % fever and cough
40 2,7%
41 2,5%
42 1,9%
43 1,5%
44 1,4%
45 1,6%
46 1,9%
47 1,4%
48 2,6%
49 2,0%
50 3,8%
51 3,9%
52 3,6%
1 3,5%
2 2,8%
3 2,5%
4 3,1%
5 3,2%
6 2,8%
7 2,6%
8 2,5%
9 2,6%
10 3,1%
11 2,6%
12 2,5%
13 2,4%
14 2,5%
15 1,9%
16 2,4%
17 2,3%
18 2,1%

Influenza Outbreak Surveillance

Outbreak activity reports were provided by all provinces and territories each week this season. Not all provinces/territories conduct influenza outbreak surveillance in all the noted facilities. A total of 1038 laboratory-confirmed influenza outbreaks were reported (Figure 7).

In addition, a total of 180 outbreaks of influenza-like illness were reported; 112 occurred in LTCF, 62 in schools, five in acute care facilities, and one in a setting categorized as “other” (e.g. retirement homes, correctional facilities, etc.)

Figure 7 – Number of influenza outbreaks by report week (all types) and number of subtyped influenza A outbreaks by subtype and report week, Canada, weeks 2018-35 to 2019-34

Figure 7

Text description
Surveillance Week A(H1N1) A(H3N2) All Types
35 0 0 0
36 0 0 0
37 0 0 0
38 0 0 0
39 0 0 0
40 2 0 3
41 0 0 0
42 0 3 3
43 2 0 4
44 4 0 4
45 1 2 6
46 7 1 11
47 3 0 7
48 8 2 14
49 3 1 7
50 11 2 21
51 14 1 21
52 7 2 34
1 20 4 62
2 18 7 55
3 9 7 44
4 7 9 41
5 7 8 38
6 5 8 43
7 2 10 35
8 5 18 66
9 2 23 54
10 2 20 60
11 5 15 52
12 2 20 56
13 1 20 57
14 0 15 46
15 0 23 50
16 0 22 34
17 0 14 30
18 0 11 26
19 1 5 17
20 0 5 9
21 0 7 9
22 0 1 2
23 0 3 7
24 0 3 3
25 0 2 2
26 0 0 1
27 0 1 1
28 0 0 0
29 0 1 1
30 0 1 1
31 0 0 0
32 0 1 1
33 0 0 0
34 0 0 0

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

Nine provinces and territories report influenza associated hospitalizations and deaths for all ages to FluWatch each week – Alberta, Manitoba, Saskatchewan, Newfoundland, Prince Edward Island, Nova Scotia, New Brunswick, Yukon and the Northwest Territories. The number of reporting provinces/territories varied over the course of the season. On average, seven provinces/territories reported each week.

A total of 3,657 influenza-associated hospitalizations were reported which corresponds to an annual seasonal hospitalization incidence of 45 hospitalizations per 100,000 population in the 2018-19 season (Table 1).

Table 1 – Estimated annual seasonal incidence of influenza hospitalizations (per 100,000 population) by age group reported by participating provinces and territoriesTable 1 Footnote 1, Canada, 2013/14 to 2018/19 influenza seasons
Age Groups (Years) Influenza Season (Predominant Influenza A Subtype)
2013-14Table 1 Footnote 2
(H1N1)
2014-15
(H3N2)
2015-16
(H1N1)
2016-17
(H3N2)
2017-18
(H3N2)
2018-19
(H1N1)
0-4 51 46 96 42 69 97
5-19 7 16 16 10 17 22
20-44 13 13 16 6 12 14
45-64 29 16 37 22 41 40
65+ 41 207 68 143 268 132
Overall 25 45 34 34 64 45
Table 1 Footnote 1

Influenza-associated hospitalizations are reported by N.L., P.E.I, N.S., N.B., Man., Alb., Y.T. and N.W.T. Data provided by Sask is not included in these rates as only hospitalizations that require intensive medical care are reported by Sask. The annual seasonal hospitalization rate for a given season is calculated using the population by age-group in participating provinces and territories.

Table 1 Return to footnote 1 referrer

Table 1 Footnote 2

During the 2013-14 season  N.B. did not report influenza-associated hospitalizations.

Table 1 Return to footnote 2 referrer

Highlighted boxes indicate the age group with the highest rate during the season.

A total of 613 ICU admissions and 224 deaths were reported this season.

Pediatric Influenza Hospitalizations and Deaths

Pediatric hospitalization data are provided by the Canadian Immunization Monitoring Program Active (IMPACT). IMPACT actively monitors pediatric influenza hospitalizations from 12 hospital sites in British Columbia, Alberta, Saskatchewan, Manitoba, Ontario, Quebec, Nova Scotia and Newfoundland.

A total of 1,352 pediatric hospitalized cases were reported this season. While the total number of hospitalized cases was above the five-year average (mean: 888; range: 593 to 1350) and the average of the last two A(H1N1)-predominant seasons (mean:1,032; range:714 to 1350), the number of hospitalized cases each week was within the expected range based on the minimum and maximum number of weekly cases observed in the previous five seasons.

Among the 1,352 pediatric hospitalized cases, a total of 271 (20%) ICU admissions and 10 (0.7%) deaths were reported. The proportion of hospitalized cases resulting in ICU admission was slightly above the average from the past five seasons (17%) and the last two A(H1N1)-predominant seasons (17%). The proportion of hospitalized cases resulting in death was consistent with the average from the past five seasons (0.6%) and slightly above the average of the last two A(H1N1)-predominant seasons (0.4%).

Figure 8 – Number of pediatric (≤16 years of age) hospitalizations reported by the IMPACT network, by region and by week of admission, Canada, weeks 2018-35 to 2019-34

Figure 8

Western hospitals consist of four sites in Vancouver, Calgary, Edmonton and Saskatoon. Central hospitals consist of 6 sites in Winnipeg, Toronto, Ottawa, Montreal and Quebec City. Eastern hospitals consist of 2 sites in Halifax & St. John's.

Text description
Surveillance Week Western Hospitals Central Hospitals Eastern Hospitals
35 0 0 0
36 0 0 0
37 0 0 0
38 0 0 0
39 0 0 0
40 0 0 0
41 <5 0 0
42 <5 <5 0
43 7 <5 0
44 18 <5 0
45 33 <5 0
46 32 5 0
47 28 7 0
48 26 20 0
49 24 17 0
50 23 29 <5
51 27 54 <5
52 28 62 <5
<5 19 70 <5
<5 14 51 0
<5 11 47 <5
<5 8 54 <5
5 9 42 <5
6 7 36 <5
7 7 35 <5
8 7 28 8
9 8 20 6
10 18 21 5
11 17 17 9
12 15 18 11
13 8 14 7
14 10 14 7
15 6 20 <5
16 15 19 <5
17 13 10 <5
18 5 19 0
19 6 13 0
20 9 7 <5
21 <5 5 <5
22 <5 7 0
23 <5 <5 0
24 <5 <5 0
25 <5 <5 0
26 0 0 <5
27 0 <5 0
28 0 0 0
29 0 0 0
30 0 <5 0
31 0 0 0
32 0 0 0
33 <5 0 0
34 0 0 0

Figure 9 – Number and percentage of pediatric hospitalizations (≤16 years of age) with influenza by age-group reported by the IMPACT network, Canada, weeks 2018-35 to 2019-34

Figure 9

Text description
Age Groups Total Number Percent Total
< 24 mo 475 35%
2-4 yr 414 31%
5-9 yr 304 22%
10-16 yr 159 12%

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 (week 44) for the 2018-19 season and ended on June 1st (week 22). CIRN-SOS collects influenza hospitalization data from eight hospital sites in Ontario, Quebec, and Nova Scotia. 

Figure 10 – Number of adult hospitalizations (≥16 years of age) with influenza reported by CIRN-SOS by surveillance week and influenza type, Canada, weeks 2018-44 to 2019-22

Figure 10

Text description
Surveillance week Influenza A Influenza B 
40 0 0
41 0 0
42 0 0
43 0 0
44 4 0
45 1 1
46 1 0
47 6 0
48 8 2
49 12 1
50 11 1
51 19 0
52 54 1
1 79 4
2 56 5
3 41 9
4 39 11
5 46 6
6 49 3
7 72 3
8 46 2
9 37 0
10 46 2
11 40 1
12 37 3
13 36 0
14 36 2
15 34 1
16 28 4
17 13 3
18 10 2
19 6 2
20 2 1
21 4 2
22 - 1
23 0 0
24 0 0

A total of 946 hospitalizations were reported by CIRN-SOS sentinels this season (age ≥16) (Figure 10):

A total of 137 (14%) ICU admissions and 65 (7%)  deaths were reported.

Figure 11 – Number and percentage of adult hospitalizations (≥16 years of age) with influenza by age group reported by CIRN-SOS, Canada, 2018-19, weeks 2018-44 to 2019-22

Figure 11

Text description
Age Group Total Number Percentage
80+ yr 297 31%
65-79 yr 270 29%
50-64 yr 203 21%
35-49 yr 85 9%
<35 yr 91 10%

Influenza Strain Characterizations

During the 2018-19 season, the National Microbiology Laboratory (NML) characterized 2,545 influenza viruses received from Canadian laboratories: 1,656 A(H1N1), 649 A(H3N2), 240 influenza B. Antigenic characterization is established by hemagglutination inhibition (HI) assay using cell-passaged vaccine reference viruses for A(H1N1) and influenza B, and the egg-passaged vaccine reference virus for A(H3N2). Over recent years, circulating strains of A(H3N2) have evolved, and are increasingly difficult to characterize by HI assay. Genetic characterization is established by sequencing the hemagglutinin gene of the influenza viruses to compare their genetic properties.

Influenza A(H3N2)

The influenza A(H3N2) component of the 2018-19 Northern Hemisphere influenza vaccine was an A/Singapore/INFIMH-16-0019/2016-like virus which belongs to the genetic group 3C.2a1.

All of the A(H3N2) viruses (649) were genetically characterized and 42% (378) of A(H3N2) viruses also grew to sufficient hemagglutination titer for antigenic characterization by HI assay (Table 2). Among all influenza A(H3N2) viruses genetically characterized, the most common subclade observed this season was 3C.2a1 (Figure 12).  Of the A(H3N2) viruses characterized antigenically by HI assay (Figure 13-A):

Table 2 – Genetic and antigenic characterization among characterized A(H3N2) viruses, Canada, weeks 2018-35 to 2019-34 (n=648)
Genetic clade Genetic charaterization only Antigenic characterization: Total A(H3N2)
Similar to
A/Singapore/INFIMH-16-0019/2016
Reduced titer to
A/Singapore/INFIMH-16-0019/2016
Clade 3C.2a 20 17 3 40
Subclade 3C.2a1 242 132 16 390
Clade 3C.3a 8 63 147 218
Total 270 212 166 648

Influenza A(H1N1)

The influenza A(H1N1) component of the 2018-19 Northern Hemisphere influenza vaccine was an A/Michigan/45/2015-like virus.

Approximately 97% (1612) of the A(H1N1) viruses characterized were antigenically similar to A/Michigan/45/2015, while only 3% (44) of viruses showed reduced titer with ferret antisera raised against cell culture-propagated A/Michigan/45/2015 (Figure 13-B).

Influenza B

The recommended influenza B components for the 2018-19 Northern Hemisphere influenza vaccine were an B/Colorado/06/2017-like virus (Victoria lineage) and a B/Phuket/3073/2013-like virus (Yamagata lineage). The B/Colorado/06/2017-like virus was included in both the trivalent and quadrivalent vaccines. The B/Phuket/3073/2013-like virus was included in the quadrivalent influenza vaccine.

The majority of B viruses characterized, 70% (168), showed reduced titer with ferret antisera raised against cell culture-propagated B/Colorado/06/2017 (Figure 13-C). Sequence analysis showed that 96% (162) of viruses that showed reduced titer had a three amino acid deletion (162-164) in the hemagglutinin gene. Of the remaining B viruses characterized, 19% (46) were characterized as B/Colorado/06/2017-like (Victoria lineage) and 11% (26) were characterized as B/Phuket/3073/2013-like (Yamagata lineage).

Figure 12 – Distribution of genetic clades among characterized influenza A(H3N2) viruses, Canada, weeks 2018-35 to 2019-34

Figure 12

Text description
Genetic Clade of A(H3N2) virus Number of viruses Percentage
Clade 3C.2a 40 6%
Subclade 3C.2a1 390 60%
Clade 3C.3a 218 34%

Figure 13 – Distribution of antigenic phenotypes among characterized influenza viruses, Canada, weeks 2018-35 to 2019-34

Figure 13

Text description
A)  A(H3N2) viruses
  Number of viruses Percentage
A/Singapore/INFIMH-16-0019/2016-like 212 56,1%
Reduced titer to A/Singapore/INFIMH-16-0019/2016 166 43,9%
Total 378 100%
B) A(H1N1) viruses
  Number of viruses Percentage
A/Michigan/45/2015-like 1612 97,3%
Reduced titer to A/Michigan/45/2015 44 2,7%
Total 1656 100%
C) B viruses
  Number of viruses Percentage
B/Colorado/06/2017-like 46 19,2%
Reduced titer to B/Colorado/06/2017 168 70,0%
B/Phuket/3073/2013-like 26 10,8%
Total 240 100%

Antiviral Resistance

All influenza viruses characterized at the NML in the 2018-19 season were resistant to amantadine and sensitive to zanamivir. All influenza A(H3N2), all influenza B viruses, and all but four A(H1N1) viruses were sensitive to oseltamivir. The four A(H1N1) viruses resistant to oseltamivir had a H275Y mutation in the viral neuraminidase. The proportion of influenza viruses resistant to oseltamivir in 2018-19 is similar to recent seasons. Since the 2009 pandemic, nearly all circulating strains of influenza have been sensitive to oseltamivir and zanamivir. Widespread resistance to amantadine among influenza A viruses has been observed for more than 10 years.

Table 3 – Proportion of characterized influenza viruses resistant to antivirals by type and subtype, Canada, 2018-35 to 2019-34
Virus type and subtype Oseltamivir Zanamivir Amantadine
# tested # resistant (%) # tested # resistant (%) # tested # resistant (%)
A (H3N2) 222 0 (0%) 222 0 (0%) 135 135 (100%)
A (H1N1) 1084 4 (0.4%) 1082 0 (0%) 391 391 (100%)
B 142 0 (0%) 142 0 (0%) NATable 3 Footnote 1 NATable 3 Footnote 1
TOTAL 1448 4 (0.3%) 1446 0 (0%) 526 526 (100%)
Table 3 Footnote 1

NA: Not Applicable

Table 3 Return to footnote 1 referrer

Vaccine Monitoring

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

The quadrivalent vaccines used in the 2018-19 northern hemisphere influenza season contained:

The B/Colorado/06/2017-like virus was included in both the trivalent and quadrivalent vaccines.

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. More detail on the methodology used for the coverage survey can be viewed here.

Overall, influenza vaccination coverage in the 2018-2019 season (42%) was significantly higher than the 2017-2018 season (38%) and the 2016-2017 season (36%). The vaccination rate was lowest among adults 18-64 years of age without any chronic medical condition (31%); however, coverage increased mostly among this subgroup when compared to the previous two seasons. Among high-risk groups, vaccination coverage rates for adults 18-64 years of age with a chronic medical condition (43%) and seniors 65 years of age and older (70%) remained steady over the past three seasons.

Table 4 – Influenza vaccine coverage among adults(≥ 18 years of age) by age group, gender and chronic diseaseTable 4 Footnote 1, Seasonal Influenza Vaccination Coverage Survey, Canada, September 2018-February 2019
Age group (years) Male Female Combined
Total Vaccine
Coverage (%)
Total Vaccine
Coverage (%)
Total Vaccine
Coverage (%)
All adults (≥18) 1568 36.6 2150 46.8 3726 41.8
18-64 All 1252 28.6 1640 39.9 2898 34.3
without chronic diseases 948 25.8 1171 36.1 2124 30.8
with chronic diseases 304 36.3 465 48.5 770 42.8
≥65 316 69.0 510 70.9 828 69.9
Table 4 Footnote 1

Excluded from stratified analysis: eight people who did not disclose their gender and four people (18-64 years old) who did not disclose whether they had any chronic diseases.

Table 4 Return to footnote 1 referrer

Vaccine Effectiveness

The Canadian Sentinel Practitioner Surveillance Network (SPSN) provides estimates of the effectiveness of the seasonal influenza vaccine in preventing primary care visits for laboratory confirmed influenza among Canadians of all ages but primarily those from 20-64 years of age.

Based on data collected between November 1, 2018 and April 30, 2019, VE against any influenza, foremost driven by A(H1N1) viruses, was 56% (95% CI: 47 to 64%), and for A(H1N1) alone was 67% (95% CI: 58 to 75%) (Table 5). This substantial protection against A(H1N1) was observed in all age groups. Conversely, the SPSN reported little or no vaccine protection against A(H3N2) viruses, with an overall VE against medically-attended outpatient A(H3N2) illness of 17% (95% CI: -13 to 39). Overall, the A(H3N2) VE estimate for 2018-19 was lower than expected generally for A(H3N2) vaccines (~30%), and similar to that observed by SPSN in the 2017-18 A(H3N2)-dominant season where VE was estimated at 14% (95% CI: -8 to 31).

More information on the SPSN including study methodology and available publications can be viewed here.

The Serious Outcomes Surveillance (SOS) Network of the Canadian Immunization Research Network (CIRN-SOS) provides estimates of the effectiveness of the seasonal influenza vaccine in preventing hospitalization for laboratory-confirmed influenza in adults.

Based on data collected between November 1, 2018 and June 1, 2019 among adult (≥16 years of age) hospitalized cases of influenza, VE against any influenza was 43% (95% CI: 28 to 55%), and for A(H1N1) alone was 68% (95% CI: 52 to 79%). CIRN-SOS also reported little or no vaccine protection against A(H3N2) viruses, with an overall VE against hospitalized  cases of influenza A(H3N2) of 19% (95% CI: -35 to 51). The number of influenza B hospitalized cases was too low to calculate an adjusted VE estimate.

More information on the CIRN-SOS Network including study methodology and available publications can be viewed here.

Table 5 – Vaccine effectiveness estimates against primary care visits (SPSN - November 1, 2018, to April 30, 2019) and hospitalizations (CIRN-SOS - November 1, 2018 to June 1, 2019)
  SPSN (Primay Care Visits)Table 5 Footnote CIRN-SOS (Adult Hospitalizations)
VE(%) (CI)Table 5 Footnote a N VE(%) (CI)Table 5 Footnote b N
All Influenza 56 (47, 64) 3034 43 (28, 55) 1350
Influenza A All 55 (46, 63) 2992 58 (43, 69) 1105
Influenza A H1N1 67 (58, 75) 2630 68 (52, 79) 562
Influenza A H3N2 17 (-13, 39) 1993 19 (-35, 51) 409
Influenza B 72 (27, 89) 1703 n/aTable 5 Footnote c 140
Table 5 Footnote †

SPSN 2018-19 estimates are published and available here https://www.ncbi.nlm.nih.gov/pubmed/30696523, and here https://www.ncbi.nlm.nih.gov/pubmed/31771709.
CI: 95% confidence interval

Table 5 Return to footnote referrer

Table 5 Footnote a

adjusted for age, province, specimen collection interval and calendar time (natural cubic spline with 3 equally spaced knots)

Table 5 Return to footnote a referrer

Table 5 Footnote b

VE for All Influenza, Influenza A, Influenza A/H1, and Influenza A/H3 was adjusted for age, pregnancy and current or past smoker.

VE for 16-49 and 50-64 age groups was adjusted for age, body mass index categories, pregnancy and medications prior to admission.

VE for 65-75 and >75 age groups was adjusted for age, Frailty index prior to admission; and current or past smoker.

Table 5 Return to footnote b referrer

Table 5 Footnote c

Sample size was too small to calculate an adjusted estimate

Table 5 Return to footnote c referrer

Provincial and International Surveillance Links

Notes

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

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