FluWatch report: May 5 to May 11, 2019 (Week 19)

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Organization: Public Health Agency of Canada

Date published: 2019-05-17

Related Topics

Overall Summary

  • Influenza activity continues to decline overall.
  • Influenza A(H3N2) was the predominant subtype this week (83% of subtyped influenza A detections); however, influenza A(H1N1)pdm09 remains the predominant subtype to date this season (71% of subtyped influenza A detections).
  • Detections of influenza A continue to be greater than those of influenza B. There is currently very little influenza B circulation compared to previous seasons.

Influenza/Influenza-like Illness Activity (geographic spread)

During week 19, the following influenza activity levels were reported (Figure 1):

  • 7 regions reported localized activity: in Ont.(4), Que.(3).
  • 29 regions reported sporadic activity: in B.C.(4), Sask.(2), Man.(5), Ont. (3), Que.(3), N.S.(2), N.B.(6), N.L.(1), Nvt. (2) and N.W.T.(1)
  • 12 regions in 9 different provinces and territories reported no activity.

Figure 1 – Map of overall influenza/ILI activity by province and territory, Canada, week 2019-19

Figure 1. Text equivalent follows.
Figure 1 - Text equivalent
Province Influenza Surveillance Region Activity Level
N.L. Eastern Sporadic
N.L. Labrador-Grenfell No Activity
N.L. Central No Activity
N.L. Western No Activity
P.E.I. Prince Edward Island No Activity
N.S. Zone 1 - Western No Activity
N.S. Zone 2 - Northern No Activity
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 Sporadic
N.B. Region 5 No Activity
N.B. Region 6 Sporadic
N.B. Region 7 Sporadic
Que. Nord-est Sporadic
Que. Québec et Chaudieres-Appalaches Sporadic
Que. Centre-du-Québec Localized
Que. Montréal et Laval Localized
Que. Ouest-du-Québec Sporadic
Que. Montérégie Localized
Ont. Central East Localized
Ont. Central West Localized
Ont. Eastern Localized
Ont. North East Localized
Ont. North West Sporadic
Ont. South West Sporadic
Ont. Toronto Sporadic
Man. Northern Regional Sporadic
Man. Prairie Mountain Sporadic
Man. Interlake-Eastern Sporadic
Man. Winnipeg Sporadic
Man. Southern Health Sporadic
Sask. North Sporadic
Sask. Central No Activity
Sask. South Sporadic
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 No Activity
Y.T. Yukon No Activity
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

In week 19, the following results were reported from sentinel laboratories across (Figures 2 and 3):

  • The percentage of tests positive for influenza increased slightly from 11% to 12% in week 19.
  • A total of 592 laboratory detections of influenza were reported, of which 76% were influenza A.
  • Influenza A(H3N2) accounted for 83% of subtyped influenza A detections.

To date this season, 47,143 laboratory-confirmed influenza detections have been reported:

  • 96% have been influenza A.
  • Among the 15,938 influenza A viruses subtyped, 71% have been A(H1N1)pdm09.
  • Influenza B often circulates later in the season in Canada (Feb-Apr). Fewer influenza B detections have been reported this season compared to recent seasons at this time of year. The percentage of tests positive for influenza B in week 19 was similar to the previous week.

To date this season, detailed information on age and type/subtype has been received for 37,844 laboratory-confirmed influenza cases (Table 1):

  • 83% of all influenza A(H1N1)pdm09 detections have been reported in individuals younger than 65 years of age.
  • 58% of all influenza A(H3N2) detections have been reported in adults 65 years of age and older.

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 2018-35 to 2019-19

Figure 2. Text equivalent follows.

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.

Figure 2 - Text equivalent
Surveillance Week A(Unsubtyped) A(H3N2) A(H1N1)pdm09 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
18 275 160 29 153
19 282 150 31 146

Figure 3 – Cumulative numbers of positive influenza specimens by type/subtype and province/territory, Canada, weeks 2018-35 to 2019-19

Figure 3. Text equivalent follows.
Figure 3 - Text equivalent
Reporting provincesTable Figure 3 - Footnote 1 Week (May 5 to May 11, 2019) Cumulative (August 26, 2018 to May 11, 2019)
Influenza A B Influenza A B A & B
Total
A
Total
A
(H1N1)pdm09
A
(H3N2)
A(UnS)Table Figure 3 - Footnote 3 B
Total
A
Total
A
(H1N1)pdm09
A
(H3N2)
A(UnS)Table Figure 3 - Footnote 3 B
Total
BC 58 3 30 25 6 6990 3153 1529 1608 229 6519
AB 95 15 62 18 21 6938 3633 1136 2169 295 6519
SK 8 2 5 1 0 2386 1387 136 863 94 2480
MB 11 0 5 6 6 1152 322 100 730 52 1202
ON 69 9 44 16 5 6236 2078 1642 2516 234 6470
QC 171 0 0 171 79 16947 0 0 16947 730 17677
NB 26 1 0 25 23 2836 231 34 2571 300 3136
NS 2 0 0 2 1 784 0 0 784 18 802
PEI 0 0 0 0 0 278 221 56 1 1 279
NL 9 0 0 9 0 1025 1 0 1024 4 1029
YT 1 0 1 0 0 115 65 15 35 0 115
N.W.T 1 0 1 0 0 179 175 4 0 2 181
NU 0 0 0 0 0 20 20 0 0 0 20
Canada 451 30 148 273 141 45186 11286 4652 29248 1957 47143
PercentageTable Figure 3 - Footnote 2 76% 7% 33% 61% 24% 96% 25% 10% 65% 4% 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 first Table Figure 3 - Footnote 3 referrer

Discrepancies in values in Figures 2 and 3 may be attributable to differing data sources.

Cumulative data includes updates to previous weeks.

Table 1 – Cumulative numbers of positive influenza specimens by type, subtype and age-group reported through case-based laboratory reporting, Canada, weeks 2018-35 to 2019-19
Age groups (years) Cumulative (August 26, 2018 to May 11, 2019)
Influenza A B Influenza A and B
A Total A(H1N1) pdm09 A(H3N2) A (UnS)Table 1 – Note 1 Total # %
0-4 6707 1689 248 4770 286 6993 18%
5-19 5127 1389 471 3267 482 5609 15%
20-44 6847 2012 596 4239 308 7155 19%
45-64 6964 1963 632 4369 115 7079 19%
65+ 10761 1480 2667 6614 247 11008 29%
Total 36406 8533 4614 23259 1438 37844 100%
Table 1 – Note 1

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

Return to Table 1 – Note 1 referrer.

Syndromic / Influenza-like Illness Surveillance

Healthcare Professionals Sentinel Syndromic Surveillance

In week 19, 0.8% of visits to healthcare professionals were due to influenza-like illness (ILI) (Figure 4).

Figure 4 – Percentage of visits for ILI reported by sentinels by report week, Canada, weeks 2018-35 to 2019-19

Number of Sentinels Reporting in Week 19: 72

Figure 4. Text equivalent follows.

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

Figure 4 - Text equivalent
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 1.8% 1.1% 0.9% 1.4%
40 0.6% 1.3% 0.9% 1.6%
41 1.1% 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 0.8% 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 1.5% 1.6% 0.8% 2.1%
49 1.6% 1.5% 1.0% 2.5%
50 1.5% 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 1.3% 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 0.5% 2.1% 1.7% 2.7%
12 1.0% 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 0.7% 1.2% 0.8% 1.6%
19 0.8% 1.3% 1.0% 1.7%

Participatory Syndromic Surveillance

FluWatchers surveillance has ended for the 2018-19 influenza season. On average 2,097 participants reported to FluWatchers each week, resulting in 64,672 questionnaires completed this season. The proportion of participants reporting fever and cough peaked in week 51 at 3.9% (Figure 5). Approximately 63% of FluWatchers participants reported being vaccinated for influenza in the 2018-19 season.

Figure 5 - Percentage of participants reporting cough and fever, Canada, weeks 2018-40 to 2019-18

Number of Participants Reporting in Week 18: 1,951

Figure 5. Text equivalent follows.
Figure 5 - Text equivalent
Surveillance Week % cough and fever
40 2.6%
41 2.5%
42 1.7%
43 1.5%
44 1.3%
45 1.7%
46 2.0%
47 1.3%
48 2.4%
49 2.0%
50 3.7%
51 3.9%
52 3.6%
1 3.4%
2 2.8%
3 2.5%
4 2.9%
5 3.0%
6 2.6%
7 2.7%
8 2.5%
9 2.7%
10 3.1%
11 2.6%
12 2.4%
13 2.4%
14 2.3%
15 1.8%
16 2.4%
17 2.3%
18 1.9%

Influenza Outbreak Surveillance

In week 19, 11 new laboratory-confirmed influenza outbreaks were reported: long-term care facilities (LTCF) (8) acute care facilities (1) and other settings (2). Four new ILI outbreaks were reported in LTCF. Among the outbreaks with available information (11), 10 were associated with influenza A (of which 2 were associated with A(H3N2)), and one outbreak was associated with influenza B.

To date this season, 838 laboratory-confirmed influenza outbreaks have been reported (Figure 6): 

  • 496 (59%) outbreaks were in LTCF, 30 were in schools and daycares, 120 in acute care facilities, and 192 were in other settings.
  • Among the 752 outbreaks for which the influenza type was available, 98% (734) were associated with influenza A.
  • Among the 323 outbreaks for which the influenza A subtype was available, 59% (192) were associated with influenza A(H3N2);

To date this season, 157 ILI outbreaks have been reported; 91 occurred in LTCF, 61 in schools, one in other settings and four in acute care facilities.

Figure 6 – Number of new outbreaks of laboratory-confirmed influenza by report week, Canada, weeks 2018-35 to 2019-19

Figure 6. Text equivalent follows.
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 0 0 0 0
39 0 0 0 0 0
40 0 2 0 1 0
41 0 0 0 0 0
42 0 2 1 0 0
43 0 3 1 0 0
44 0 1 1 2 0
45 0 2 1 3 0
46 2 5 1 3 0
47 2 4 0 1 0
48 2 6 1 5 0
49 1 2 3 1 0
50 3 9 5 4 0
51 3 12 4 2 0
52 4 25 5 0 0
1 5 40 11 0 0
2 8 38 7 0 0
3 3 27 10 0 0
4 6 19 10 1 0
5 6 24 6 0 0
6 9 22 7 0 0
7 6 20 7 0 0
8 5 30 11 4 0
9 9 23 14 2 0
10 12 26 8 1 0
11 4 24 14 0 0
12 9 22 15 0 0
13 8 23 11 0 0
14 3 22 6 0 0
15 6 19 8 0 0
16 0 15 10 0 0
17 1 11 8 0 0
18 1 9 4 0 0
19 1 8 2 0 0

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

To date this season, 3,092 influenza-associated hospitalizations have been reported by participating provinces and territoriesFootnote 1. Note that data from one participating jurisdiction has not been available since surveillance week 13, so these figures are an underestimate of cases for this season.

Hospitalizations (Table 2):

  • 97.6% (3,018) were associated with influenza A
  • Among the 1,704 cases for which the influenza subtype was available, 1,414 (83%) were associated with A(H1N1)pdm09.
  • The highest estimated rate of hospitalization is among adults over 65 years of age.

Intensive Care Unit (ICU) cases and deaths:

  • To date this season 555 ICU admissions and 182 deaths have been reported.
    • 41% (227) of reported ICU admissions were in adults aged 45-64 years.
    • All but eight ICU admissions were associated with influenza A.
    • All but one of the deaths were associated with influenza A.
Table 2 – Cumulative number and estimated rate of hospitalizations by age-group reported by participating provinces and territoriesFootnote 1, Canada, weeks 2018-35 to 2019-19
Age Groups (years) Cumulative (August 26, 2018 to May 11, 2019)
Influenza A Influenza B Rate per 100,000 population
0-4 394 23 87.61
5-19 235 20 18.38
20-44 354 10 12.79
45-64 776 7 35.98
65+ 1259 14 104.63
Total 3018 74  
% 97.6% 2.4%  
Table 2 – Note 1

Influenza-associated hospitalizations are reported by N.L., P.E.I, N.S., N.B., Man., Alb., Y.T. and N.W.T. Only hospitalizations that require intensive medical care are reported by Sask. The cumulative rate of hospitalizations is calculated using the population by age-group in participating provinces and territories.

Return to Table 2 – Note 1

Pediatric Influenza Hospitalizations and Deaths

To date this season, 1,280 pediatric hospitalizations have been reported (Figure 7 & 8):

  • 66% of cases were in children under 5 years of age.
  • 93% (1,192) of cases have been associated with influenza A.
  • Among the 375 cases for which the influenza subtype was available, 305 (81%) were associated with A(H1N1)pdm09.

To date this season, 246 ICU admissions, and 10 deaths have been reported.

  • 58% (142) of ICU admissions were in children under 5 years of age.
  • All but 13 (95%) of the ICU admissions have been associated with influenza A; 84% of the 105 cases for which the influenza A subtype was available were associated with A(H1N1)pdm09.
  • 80% (8) of deaths occurred in children 2 to 4 years of age.
  • All deaths have been associated with influenza A.

Figure 7 – Number of pediatric (≤16 years of age) hospitalizations reported by the IMPACT network, by week, Canada, weeks 2018-35 to 2019-19

Figure 7. Text equivalent follows.

The shaded area represents the maximum and minimum number of cases reported by week from seasons 2010-11 to 2017-18

Figure 7 - Text equivalent
Surveillance week 2018-19 Average Min Max
35 0 0 0 0
36 0 0 0 1
37 0 0 0 2
38 0 0 0 2
39 0 1 0 3
40 0 0 0 2
41 1 1 0 2
42 5 1 0 4
43 12 1 0 3
44 15 3 1 6
45 37 3 2 4
46 41 5 1 13
47 37 4 0 9
48 40 9 2 23
49 46 15 3 28
50 51 23 4 47
51 84 32 4 72
52 89 47 7 92
1 91 40 5 75
2 62 35 4 62
3 64 38 4 67
4 66 35 7 47
5 49 40 11 59
6 46 38 15 79
7 48 40 17 120
8 42 47 25 139
9 34 50 13 153
10 45 48 17 135
11 42 41 18 118
12 42 33 13 89
13 29 32 14 67
14 34 24 12 56
15 28 23 13 56
16 34 20 10 41
17 29 16 8 37
18 22 14 4 28
19 17 10 5 18

Figure 8 - Cumulative numbers of pediatric hospitalizations (≤16 years of age) with influenza by age-group reported by the IMPACT network, Canada, weeks 2018-35 to 2019-19

Figure 8. Text equivalent follows.
Figure 8 - Text equivalent
Age Group Total
0-5 mo 138
6-23 mo 318
2-4 yr 389
5-9 yr 285
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 2018-19 season.

To date this season, 942 hospitalizations, 115 ICU admissions and 54 deaths have been reported (Figure 9):

  • 873 (93%) hospitalizations were associated with influenza A.
  • A greater proportion of hospitalizations have been reported among adults ≥65 years of age (60%) compared to adults <65 years of age (40%).
  • Among the 204 cases for which the influenza subtype was available, 107 (52%) were associated with A(H1N1)pdm09.
  • 86% of hospitalized cases reported more than one type of comorbid condition.
  • The most commonly reported comorbidity was endocrine disorders, which were reported in 87% of hospitalized cases.

Figure 9 - Cumulative numbers of adult hospitalizations (>20 years of age) with influenza by age-group reported by CIRN, Canada, 2018-19, weeks 2018-44 to 2019-19

Figure 9. Text equivalent follows.
Figure 9 - Text equivalent
Age Group Total
20-34 yr 92
35-49 yr 84
50-64 yr 199
65-79 yr 271
80+ yr 296

Influenza Strain Characterizations

From September 1, 2018 to 16 May, 2019, the National Microbiology Laboratory (NML) has characterized 2 170 influenza viruses (440 A(H3N2), 1,594 A(H1N1) and 136 B) that were received from Canadian laboratories.

Genetic Characterization of Influenza A(H3N2):

191 influenza A(H3N2) viruses did not grow to sufficient hemagglutination titer for antigenic characterization by hemagglutination inhibition (HI) assay. Therefore, NML has performed genetic characterization to determine the genetic group identity of these viruses.

Sequence analysis of the HA gene of the viruses showed that:

  • 20 viruses belonged to genetic group 3C.2a.
  • 168 viruses belonged to subclade 3C.2a1.
  • Four viruses belonged to 3C.3a.
  • One isolate could not be sequenced.

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

Antigenic Characterization:

Influenza A (H3N2):

  • 148 influenza A(H3N2) viruses were antigenically characterized as A/Singapore/INFIMH-16-0019/2016-like by HI testing using antiserum raised against egg-propagated A/Singapore/INFIMH-16-0019/2016.
  • 99 viruses showed reduced titer with ferret antisera raised against egg-propagated A/Singapore/INFIMH-16-0019/2016.
  • A/Singapore/INFIMH-16-0019/2016-like virus is the influenza A(H3N2) component of the 2018-19 Northern Hemisphere influenza vaccine.
  • 101 influenza A(H3N2) viruses characterized belonged to genetic group 3C.2a1. 20 viruses belonged to genetic group 3C.2a and 116 to 3C.3a. Sequencing is pending for the remaining isolates.

Influenza A(H1N1):

  • 1,551 A(H1N1) viruses characterized were antigenically similar to A/Michigan/45/2015, which is the influenza A(H1N1) component of the 2018-19 Northern Hemisphere influenza vaccine.
  • 43 viruses showed reduced titer with ferret antisera raised against cell culture-propagated A/Michigan/45/2015

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 2018-19 Northern Hemisphere influenza vaccine are B/Colorado/06/2017 (Victoria lineage) and B/Phuket/3073/2013 (Yamagata lineage).

  • 25 influenza B viruses were characterized as B/Colorado/06/2017, which belong to the Victoria lineage and are included as an influenza B component of the 2018-19 Northern Hemisphere influenza vaccine.
  • 88 viruses showed reduced titer with ferret antisera raised against cell culture-propagated B/Colorado/06/2017. Sequence analysis showed that 87 viruses that showed reduced titer had a three amino acid deletion (162-164) in the HA gene.
  • 23 influenza B viruses were characterized as B/Phuket/3073/2013-like, which belongs to the Yamagata lineage and is included as an influenza B component of the 2018-19 Northern Hemisphere quadrivalent influenza vaccine.

Antiviral Resistance

Antiviral Resistance – Amantadine:

449 influenza A (89 A(H3N2) and 360 A(H1N1)) viruses were tested for resistance to amantadine and it was found that:

  • All 449 influenza A viruses were resistant to amantadine.

Antiviral Resistance – Oseltamivir:

1,262 influenza viruses (159 A(H3N2), 1,024 A(H1N1) and 79 B) were tested for resistance to oseltamivir and it was found that:

  • All 159 A(H3N2) viruses were sensitive to oseltamivir.
  • Of the 1,024 A(H1N1) viruses tested, 1,020 were sensitive to oseltamivir and four viruses were resistant to oseltamivir with a H275Y mutation.
  • All 79 B viruses were sensitive to oseltamivir.

Antiviral Resistance – Zanamivir:

1,261 influenza viruses (159 A(H3N2), 1,023 H1N1 and 79 B) were tested for resistance to zanamivir and it was found that:

  • All 1,261 influenza viruses were sensitive to zanamivir.

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 related to the influenza vaccine in Canada. This survey measures vaccine coverage, which is the percentage of people who received the annual seasonal influenza vaccine in a specific influenza season.

In the 2018-19 influenza season, coverage was:

  • 34% among adults aged 18 to 64 years.
    • 31% among adults aged 18-64 wihout chronic diseases.
    • 43% among adults aged 18 to 64 years with chronic diseases.
  • 70% among seniors (aged 65 years and older).
Table 3 – Influenza vaccine coverage among adults (≥ 18 years of age) by age group, gender and chronic diseaseTable 3 – Note 1, Seasonal Influenza Vaccination Coverage Survey, Canada, October 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 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 3 – Note 1

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

Return to Table 3 – Note 1 referrer.

Vaccine Effectiveness

Vaccine effectiveness (VE) is a measure of how well the influenza vaccine is able to prevent influenza illness. Throughout the influenza season, surveillance networks estimate how well the influenza vaccine is working. Estimates can vary depending on several factors such as the study methods; the population, setting and outcomes that are being studied; the type and mix of vaccine products; the stage of the season and the kinds of influenza viruses that are circulating when the study is conducted.

The community-based Canadian Sentinel Practitioner Surveillance Network (SPSN) published an interim VE estimate in January 2019 for A(H1N1)pdm09. Subsequently, given an atypical late-season wave of influenza A(H3N2),SPSN has undertaken an additional interim analysis to assess effectiveness of the 2018/19 influenza vaccine against medically-attended outpatient A(H3N2) illness. Vaccine effectiveness (VE) monitoring methods and results are available at the SPSN website.

Based on data collected as of March 30th, 2019 from more than 2800 patients from B.C., Alta., Ont., and Que., the 2018/19 northern hemisphere vaccine effectiveness has varied depending on the strain.

  • A(H1N1)pdm09: In the first interim analysis, VE against A(H1N1)pdm09 was 72% (95% CI: 60 to 81) overall, with substantial protection observed in all age groups. In the most recent analysis as of March 30th, estimates against A(H1N1)pmd09 have remained stable at approximately 70%.
  • A(H3N2): In the most recent analysis, VE against A(H3N2) was 23% (95% CI: -9 to 46) overall. As the confidence interval crosses zero, this estimate does not provide evidence of vaccine protection against medically-attended outpatient A(H3N2) illness.

The SPSN continues to monitor and will further update VE estimates at end of season.

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