FluWatch report: April 14 to April 20, 2019 (Week 16)

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	Sporadic
N.S.	Zone 1 - Western	Sporadic
N.S.	Zone 2 - Northern	Sporadic
N.S.	Zone 3 - Eastern	Localized
N.S.	Zone 4 - Central	Localized
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	Sporadic
N.B.	Region 7	Sporadic
Que.	Nord-est	Sporadic
Que.	Québec et Chaudieres-Appalaches	Sporadic
Que.	Centre-du-Québec	Sporadic
Que.	Montréal et Laval	Sporadic
Que.	Ouest-du-Québec	Localized
Que.	Montérégie	Localized
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 Activity
Man.	Prairie Mountain	Localized
Man.	Interlake-Eastern	Sporadic
Man.	Winnipeg	Sporadic
Man.	Southern Health	Sporadic
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	Localized
N.W.T.	North	No Activity
N.W.T.	South	Sporadic
Nvt.	Qikiqtaaluk	No Data
Nvt.	Kivalliq	No Data
Nvt.	Kitimeot	No Data

Laboratory-Confirmed Influenza Detections

In week 16, the following results were reported from sentinel laboratories across Canada (Figures 2 and 3):

• The percentage of tests positive for influenza decreased to 17% in week 16.
• A total of 1,024 laboratory detections of influenza were reported, of which 85% were influenza A.
• Influenza A(H3N2) accounted for 89% of subtyped influenza A detections.

To date this season, 44,970 laboratory-confirmed influenza detections have been reported:

• 97% have been influenza A.
• Among the 15,235 influenza A viruses subtyped, 73% 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 36,036 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.

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	618	261	38	166

Figure 3 - Text equivalent

Reporting provincesTable Figure 3 - Footnote 1	Week (April 7 to April 20, 2019)					Cumulative (August 26, 2018 to April 20, 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	117	17	48	52	13	6160	3124	1426	1610	208	6368
AB	144	10	101	33	18	6596	3598	903	2095	228	6824
SK	0	0	0	0	0	2333	1378	104	851	75	2408
MB	12	1	6	5	5	1107	312	71	724	25	1132
ON	159	3	93	63	18	5953	2052	1469	2432	190	6143
QC	301	0	0	301	61	16345	0	0	16345	502	16847
NB	59	0	0	59	35	2722	230	34	2458	209	2931
NS	21	0	0	21	1	759	0	0	759	15	774
PEI	2	0	2	0	0	273	220	52	1	0	273
NL	52	0	0	52	1	971	1	0	970	4	975
YT	4	0	0	4	0	99	54	12	33	0	99
N.W.T	1	1	0	0	0	175	173	2	0	1	176
NU	0	0	0	0	0	20	20	0	0	0	20
Canada	872	32	250	590	152	43513	11162	4073	28278	1457	44970
PercentageTable Figure 3 - Footnote 2	85%	4%	29%	68%	15%	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 2019-16

Age groups (years)	Cumulative (August 26, 2018 to April 20, 2019)
	Influenza A				B	Influenza A and B
	A Total	A(H1N1) pdm09	A(H3N2)	A (UnS)Table 1 – Note 1	Total	#	%
0-4	6566	1679	213	4674	195	6761	19%
5-19	4967	1387	416	3164	330	5297	15%
20-44	6661	1990	536	4135	230	6891	19%
45-64	6757	1950	549	4258	92	6849	19%
65+	10027	1452	2341	6234	211	10238	28%
Total	34978	8458	4055	22465	1058	36036	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

Syndromic / Influenza-like Illness Surveillance

Healthcare Professionals Sentinel Syndromic Surveillance

In week 16, 0.8% of visits to healthcare professionals were due to influenza-like illness (ILI) (Figure 4).

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	0.9%	1.6%	0.9%	1.9%
16	0.8%	1.5%	1.0%	1.9%

Participatory Syndromic Surveillance

In week 16, 1,904 participants reported to FluWatchers, of which 46 (2.4%) reported symptoms of cough and fever (Figure 5).

Among the 46 participants who reported fever and cough:

• 13% consulted a healthcare professional;
• 65% reported days missed from work or school, resulting in a combined total of 92 missed days of work or school.

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%

Influenza Outbreak Surveillance

In week 16, 21 new laboratory-confirmed influenza outbreaks were reported: long-term care facilities (LTCF) (12) and other settings (9). Three new ILI outbreaks were reported: LTCF (2) and schools (1). Among the outbreaks with available subtype information (7), all were associated with influenza A(H3N2).

To date this season, 753 laboratory-confirmed influenza outbreaks have been reported (Figure 6):

• 441 (59%) outbreaks were in LTCF, 30 were in schools and daycares, 113 in acute care facilities, and 169 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, 151 ILI outbreaks have been reported; 85 occurred in LTCF, 61 in schools, one in other settings and four in acute care facilities.

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	18	4	0	0
15	6	15	7	0	0
16	0	12	9	0	0

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

To date this season, 2,932 influenza-associated hospitalizations have been reported by participating provinces and territories^{Footnote 1}.

Hospitalizations (Table 2):

• 98.4% (2,886) were associated with influenza A
• Among the 1,670 cases for which the influenza subtype was available, 1,404 (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 536 ICU admissions and 165 deaths have been reported.
  • 41% (221) of reported ICU admissions were in adults aged 45-64 years.
  • All but seven 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 territories^{Footnote 1}, Canada, weeks 2018-35 to 2019-16

Age Groups (years)	Cumulative (August 26, 2018 to April 20, 2019)
	Influenza A	Influenza B	Rate per 100,000 population
0-4	383	17	84.04
5-19	231	15	17.73
20-44	345	4	12.27
45-64	748	3	34.51
65+	1179	7	97.48
Total	2886	46
%	98.4%	1.6%
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, 1,217 pediatric hospitalizations have been reported (Figure 7 & 8):

• 66% of cases were in children under 5 years of age.
• 95% (1,152) of cases have been associated with influenza A.
• Among the 358 cases for which the influenza subtype was available, 299 (84%) were associated with A(H1N1)pdm09.

To date this season, 229 ICU admissions, and 10 deaths have been reported.

• 59% (135) of ICU admissions were in children under 5 years of age.
• All but nine 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.

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	84	32	4	72
52	89	47	7	92
1	92	40	5	75
2	61	35	4	62
3	65	38	4	67
4	66	35	7	47
5	49	40	11	59
6	47	38	15	79
7	46	40	17	120
8	45	47	25	139
9	35	50	13	153
10	46	48	17	135
11	41	41	18	118
12	42	33	13	89
13	29	32	14	67
14	34	24	12	56
15	28	23	13	56
16	33	20	10	41

Figure 8 - Text equivalent

Age Group	Total
0-5 mo	130
6-23 mo	308
2-4 yr	367
5-9 yr	270
10-16 yr	142

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 1^st for the 2018-19 season.

To date this season, 901 hospitalizations, 105 ICU admissions and 50 deaths have been reported (Figure 9):

• 840 (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 194 cases for which the influenza subtype was available, 106 (55%) were associated with A(H1N1)pdm09.
• 89% 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 - Text equivalent

Age Group	Total
20-34 yr	86
35-49 yr	82
50-64 yr	190
65-79 yr	263
80+ yr	280

Influenza Strain Characterizations

Since September 1, 2018, the National Microbiology Laboratory (NML) has characterized 2,006 influenza viruses (353 A(H3N2), 1,553 A(H1N1) and 100 B) that were received from Canadian laboratories.

Genetic Characterization of Influenza A(H3N2):

164 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.
• 139 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):

• 111 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.
• 78 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.
• 71 influenza A(H3N2) viruses characterized belonged to genetic group 3C.2a1. 18 viruses belonged to genetic group 3C.2a and 29 to 3C.3a. Sequencing is pending for the remaining isolates.

Influenza A(H1N1):

• 1,510 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.
• 61 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:

428 influenza A (77 A(H3N2) and 351 A(H1N1)) viruses were tested for resistance to amantadine and it was found that:

• All 428 influenza A viruses were resistant to amantadine.

Antiviral Resistance – Oseltamivir:

1,183 influenza viruses (134 A(H3N2), 989 A(H1N1) and 60 B) were tested for resistance to oseltamivir and it was found that:

• All 134 A(H3N2) viruses were sensitive to oseltamivir.
• Of the 989 A(H1N1) viruses tested, 985 were sensitive to oseltamivir and four viruses were resistant to oseltamivir with a H275Y mutation.
• All 60 B viruses were sensitive to oseltamivir.

Antiviral Resistance – Zanamivir:

1,182 influenza viruses (134 A(H3N2), 988 H1N1 and 60 B) were tested for resistance to zanamivir and it was found that:

• All 1,182 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 disease^{Table 3 – Note 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	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

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 30^th, 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.