FluWatch report: April 7 to April 13, 2019 (Week 15)

thumbnail

Download the alternative format
(PDF format, 902 KB, 10 pages)

Organization: Public Health Agency of Canada

Date published: 2019-04-18

Related Topics

Overall Summary

  • Due to the shortened reporting week, not all data providers were able to report their data.
  • A second smaller wave of sustained influenza activity, dominated by A(H3N2), continues to be observed in Canada.
  • Detections of influenza A(H3N2) have been steadily increasing since mid-January and accounted for 83% of subtyped influenza A detections this week; however, influenza A(H1N1)pdm09 remains the predominant subtype to date this season.
  • 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.
  • For more information on Canadian estimates of vaccine coverage and effectiveness, please see the new vaccine monitoring section in the FluWatch report.

Influenza/Influenza-like Illness Activity (geographic spread)

During week 15, the following influenza activity levels were reported (Figure 1):

  • 12 regions reported localized activity: in Sask.(1), Ont.(7), Que.(1), N.B.(2) and P.E.I.(1).
  • 19 regions reported sporadic activity: in B.C.(5), Sask.(2), Que.(5), N.B.(5), Y.T.(1) and N.W.T.(1)
  • One region: in N.W.T.(1) reported no activity.

Figure 1 – Map of overall influenza/ILI activity by province and territory, Canada, week 2019-15

Figure 1. Text equivalent follows.
Figure 1 - Text equivalent
Province Influenza Surveillance Region Activity Level
N.L. Eastern No Data
N.L. Labrador-Grenfell No Data
N.L. Central No Data
N.L. Western No Data
P.E.I. Prince Edward Island Localized
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 Localized
N.B. Region 2 Sporadic
N.B. Region 3 Sporadic
N.B. Region 4 Sporadic
N.B. Region 5 Sporadic
N.B. Region 6 Localized
N.B. Region 7 Sporadic
Que. Nord-est Sporadic
Que. Québec et Chaudieres-Appalaches Sporadic
Que. Centre-du-Québec Localized
Que. Montréal et Laval Sporadic
Que. Ouest-du-Québec Sporadic
Que. Montérégie Sporadic
Ont. Central East Localized
Ont. Central West Localized
Ont. Eastern Localized
Ont. North East Localized
Ont. North West Localized
Ont. South West Localized
Ont. Toronto Localized
Man. Northern Regional No Data
Man. Prairie Mountain No Data
Man. Interlake-Eastern No Data
Man. Winnipeg No Data
Man. Southern Health No Data
Sask. North Sporadic
Sask. Central Localized
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 Sporadic
Y.T. Yukon Sporadic
N.W.T. North Sporadic
N.W.T. South No Activity
Nvt. Qikiqtaaluk No Data
Nvt. Kivalliq No Data
Nvt. Kitimeot No Data

Laboratory-Confirmed Influenza Detections

In week 15, the following results were reported from sentinel laboratories across Canada (Figures 2 and 3):

  • The percentage of tests positive for influenza remained steady at 20%.
  • A total of 1,512 laboratory detections of influenza were reported, of which 90% were influenza A.
  • Influenza A(H3N2) accounted for 83% of subtyped influenza A detections.

To date this season, 43,904 laboratory-confirmed influenza detections have been reported:

  • 97% have been influenza A.
  • Among the 14,896 influenza A viruses subtyped, 74% 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.

To date this season, detailed information on age and type/subtype has been received for 35,175 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.
  • 57% 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 2019-15

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
15 811 492 104 156

Figure 3 – Cumulative numbers of positive influenza specimens by type/subtype and province/territory, Canada, weeks 2018-35 to 2019-15

Figure 3. Text equivalent follows.
Figure 3 - Text equivalent
Reporting
provincesTable Figure 3 - Footnote 1
Week (April 7 to April 13, 2019) Cumulative (August 26, 2018 to April 13, 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 390 78 243 69 19 6072 3098 1371 1603 195 6267
AB 147 5 110 32 21 6424 3586 786 2052 209 6633
SK 0 0 0 0 0 2295 1374 93 828 70 2365
MB 21 3 11 7 1 1096 308 64 724 20 1116
ON 214 10 109 95 21 5794 2045 1376 2373 172 5966
QC 400 0 0 400 46 16044 0 0 16044 441 16485
NB 50 0 0 50 42 2663 230 34 2399 174 2837
NS 29 0 0 29 1 738 0 0 738 14 752
PEI 8 1 7 0 0 271 220 50 1 0 271
NL 97 0 0 97 0 919 1 0 918 3 922
YT 3 1 1 1 0 95 54 12 29 0 95
N.W.T 2 2 0 0 0 174 172 2 0 1 175
NU 0 0 0 0 0 20 20 0 0 0 20
Canada 1361 100 481 780 151 42605 11108 3788 27709 1299 43904
PercentageTable Figure 3 - Footnote 2 90% 7% 35% 57% 10% 97% 26% 9% 65% 3% 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 2019-15
Age groups (years) Cumulative (August 26, 2018 to April 13, 2019)
Influenza A B Influenza A and B
A Total A(H1N1) pdm09 A(H3N2) A (UnS)Table 1 – Note 1 Total # %
0-4 6481 1675 186 4620 173 6654 19%
5-19 4867 1384 382 3101 282 5149 15%
20-44 6548 1979 509 4060 204 6752 19%
45-64 6650 1935 520 4195 89 6739 19%
65+ 9682 1439 2191 6052 199 9881 28%
Total 34228 8412 3788 22028 947 35175 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 15, 1.0% 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 2019-15

Number of Sentinels Reporting in Week 15: 81

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 1.2% 1.7% 1.2% 2.6%
14 1.0% 1.8% 1.3% 2.4%
15 1.0% 1.6% 0.9% 1.9%

Participatory Syndromic Surveillance

In week 15, 2,013 participants reported to FluWatchers, of which 36 (1.8%) reported symptoms of cough and fever (Figure 5).

Among the 36 participants who reported fever and cough:

  • 28% consulted a healthcare professional;
  • 69% reported days missed from work or school, resulting in a combined total of 72 missed days of work or school.

Figure 5 - Percentage of participants reporting cough and fever, Canada, weeks 2018-40 to 2019-15

Number of Participants Reporting in Week 15: 2,013

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%

Influenza Outbreak Surveillance

In week 15, 22 new laboratory-confirmed influenza outbreaks were reported: long-term care facilities (LTCF) (9), acute care facilities (6) and other settings (7). No new ILI outbreaks were reported. Among the outbreaks with available subtype information (4), all were associated with influenza A(H3N2).

To date this season, 739 laboratory-confirmed influenza outbreaks have been reported (Figure 6):

  • 433 (59%) outbreaks were in LTCF, 30 were in schools and daycares, 113 in acute care facilities, and 163 were in other settings.
  • Among the 662 outbreaks for which the influenza type was available, 98% (648) were associated with influenza A.
  • Among the 281 outbreaks for which the influenza A subtype was available, 54% (151) were associated with influenza A(H3N2);

To date this season, 145 ILI outbreaks have been reported; 81 occurred in LTCF, 59 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 2019-15

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 5 23 7 0 0
6 9 21 7 0 0
7 6 20 7 0 0
8 5 30 11 4 0
9 9 23 13 2 0
10 12 26 8 1 0
11 3 23 14 0 0
12 8 22 13 0 0
13 8 23 11 0 0
14 3 16 4 0 0
15 6 9 7 0 0

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

To date this season, 2,859 influenza-associated hospitalizations have been reported by participating provinces and territoriesFootnote 1.

Hospitalizations (Table 2):

  • 98.4% (2,811) were associated with influenza A
  • Among the 1,643 cases for which the influenza subtype was available, 1,387 (84%) 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 513 ICU admissions and 148 deaths have been reported.
    • 42% (211) of reported ICU admissions were in adults aged 45-64 years.
    • All but six 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 2019-15
Age Groups (years) Cumulative (August 26, 2018 to April 13, 2019)
Influenza A Influenza B Rate per 100,000 population
0-4 378 17 82.99
5-19 226 15 17.37
20-44 338 5 12.06
45-64 735 4 33.96
65+ 1134 7 93.78
Total 2811 48  
% 98.3% 1.7%  
Table 2 – Note 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. The cumulative rate of hospitalizations is calculated using the total population by age-group in participating provinces and territories.

Return to Table 2 – Note 1

Pediatric Influenza Hospitalizations and Deaths

To date this season, 1,147 pediatric hospitalizations have been reported (Figure 7 & 8):

  • 67% of cases were in children under 5 years of age.
  • 96% (1,098) of cases have been associated with influenza A.
  • Among the 335 cases for which the influenza subtype was available, 290 (87%) were associated with A(H1N1)pdm09.

To date this season, 203 ICU admissions, and 10 deaths have been reported.

  • 60% (122) of ICU admissions were in children under 5 years of age.
  • All but six of the ICU admissions have been associated with influenza A.
  • 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 2019-14

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 36 4 0 9
48 40 9 2 23
49 46 15 3 28
50 51 23 4 47
51 83 32 4 72
52 89 47 7 92
1 90 40 5 75
2 62 35 4 62
3 70 38 4 67
4 60 35 7 47
5 49 40 11 59
6 47 38 15 79
7 43 40 17 120
8 43 47 25 139
9 35 50 13 153
10 46 48 17 135
11 42 41 18 118
12 42 33 13 89
13 31 32 14 67
14 31 24 12 56

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 2019-14

Figure 8. Text equivalent follows.
Figure 8 - Text equivalent
Age Group Total
0-5 mo 120
6-23 mo 296
2-4 yr 354
5-9 yr 252
10-16 yr 125

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, 847 hospitalizations, 103 ICU admissions and 46 deaths have been reported (Figure 9):

  • 790 (93%) hospitalizations were associated with influenza A.
  • A greater proportion of hospitalizations have been reported among adults ≥65 years of age (59%) compared to adults <65 years of age (41%).
  • Among the 182 cases for which the influenza subtype was available, 106 (58%) were associated with A(H1N1)pdm09.
  • 88% of hospitalized cases reported more than one type of comorbid condition.
  • The most commonly reported comorbidity was endocrine disorders, which were reported in 95% 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 2019-14

Figure 9. Text equivalent follows.
Figure 9 - Text equivalent
Age Group Total
20-34 yr 80
35-49 yr 79
50-64 yr 186
65-79 yr 247
80+ yr 255

Influenza Strain Characterizations

Since September 1, 2018, the National Microbiology Laboratory (NML) has characterized 1,904 influenza viruses (314 A(H3N2), 1,523 A(H1N1) and 67 B) that were received from Canadian laboratories.

Genetic Characterization of Influenza A(H3N2):

155 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.
  • 131 viruses belonged to subclade 3C.2a1.
  • Three 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):

  • 103 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.
  • 53 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.
  • 67 influenza A(H3N2) viruses characterized belonged to genetic group 3C.2a1. 17 viruses belonged to genetic group 3C.2a and 29 to 3C.3a. Sequencing is pending for the remaining isolates.

Influenza A(H1N1):

  • 1,480 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).

  • 16 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.
  • 28 viruses showed reduced titer with ferret antisera raised against cell culture-propagated B/Colorado/06/2017.
  • 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:

416 influenza A (73 A(H3N2) and 343 A(H1N1)) viruses were tested for resistance to amantadine and it was found that:

  • All 416 influenza A viruses were resistant to amantadine.

Antiviral Resistance – Oseltamivir:

1,096 influenza viruses (112 A(H3N2), 933 A(H1N1) and 51 B) were tested for resistance to oseltamivir and it was found that:

  • All 112 A(H3N2) viruses were sensitive to oseltamivir.
  • Of the 933 A(H1N1) viruses tested, 929 were sensitive to oseltamivir and four viruses were resistant to oseltamivir with a H275Y mutation.
  • All 51 B viruses were sensitive to oseltamivir.

Antiviral Resistance – Zanamivir:

1,095 influenza viruses (112 A(H3N2), 932 H1N1 and 51 B) were tested for resistance to zanamivir and it was found that:

  • All 1,095 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.

Report a problem or mistake on this page
Please select all that apply:

Thank you for your help!

You will not receive a reply. For enquiries, contact us.

Date modified: