FluWatch report: November 17 to 23, 2019 (week 47)

Influenza/Influenza-like Illness Activity (geographic spread)

During week 47, levels of influenza activity were similar to the previous week (Figure 1).

• Activity was reported across 10 provinces and territories.
• Among regions with influenza activity, 25 reported a sporadic level of activity, and 4 reported localized activity.

Figure 1 - Text equivalent

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

Laboratory-Confirmed Influenza Detections

In week 47, the number of detections of influenza continued to increase. The following results were reported from sentinel laboratories across Canada (Figures 2 and 3):

• The percentage of tests positive for influenza is at the seasonal threshold of 5%. This is consistent with the median week that laboratory detections of influenza crossed the seasonal threshold over the previous five seasons.
• Compared to the past five seasons, the percentage of tests positive for influenza is slightly below average (8.3%) for this time of year.
• A total of 298 laboratory detections of influenza were reported, of which 61% (183) were influenza A.
• Both the proportion of detections of influenza B (39%) and the percentage of tests positive for influenza B (1.9%) are higher than the average for this time of year. The current level of influenza B activity is not normally seen until early-January.
• Among subtyped influenza A detections, a mix of A(H1N1) and A(H3N2) were detected; 55% (40 out of 72) were influenza A(H3N2).

To date this season (weeks 35 to 47), 1,258 laboratory detections of influenza were reported:

• 76% (954) were influenza A. The proportion of detections of influenza B to date (24%) is higher than average (8.5%); and higher than was observed during the 2017-18 season (16 %) when influenza A and B circulated in almost equal proportions,
• Among subtyped influenza A detections (405), 73% were influenza A(H3N2).

Detailed information on age and type/subtype has been received for 1,017 laboratory-confirmed influenza cases (Table 1).

To date this season (weeks 35 to 47):

• Among cases of influenza A(H3N2) (265), the largest proportion were in adults 65 years of age and older (44%).
• Cases of influenza B (270) were primarily in younger age groups; 54% of cases were under 20 years of age and 33% between 20 and 44 years of age.
• Among cases of influenza A(H1N1) (95), the largest proportion were in adults between 45 and 64 years of age (37%).

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 - Text equivalent

Surveillance Week	A(Unsubtyped)	A(H3N2)	A(H1N1)pdm09	Influenza B	Percent Positive A	Percent Positive B
35	10	16	0	2	1.3	0.1
36	11	13	2	2	1.1	0.1
37	5	17	2	5	0.9	0.2
38	11	15	3	6	1.0	0.2
39	11	21	2	3	1.0	0.1
40	34	9	1	2	1.2	0.1
41	34	18	0	5	1.4	0.1
42	54	12	1	14	1.6	0.3
43	44	13	7	17	1.6	0.3
44	43	23	16	17	1.8	0.3
45	57	57	20	39	2.2	0.7
46	82	43	22	77	2.7	1.4
47	101	40	32	115	3.1	1.9

Figure 3 - Text equivalent

Provinces Table Figure 3 - Footnote 1	Cumulative (August 25, 2019 to November 23, 2019)
	A Total	A(H1N1)	A(H3N2)	A(UnS)Table Figure 3 - Footnote 3	B Total	A & B Total
B.C.	203	12	74	65	14	217
Alta.	275	59	135	81	154	429
Sask.	60	0	0	36	12	72
Man.	34	10	10	14	30	64
Ont.	104	21	53	30	30	134
Que.	231	0	0	231	58	289
N.B.	11	2	2	7	2	13
N.S.	2	0	0	2	1	3
P.E.I.	1	0	0	1	2	3
N.L.	17	0	15	2	1	18
Y.T.	11	0	8	3	0	11
N.W.T	5	4	0	1	0	5
Nvt.	0	0	0	0	0	0
Canada	954	108	297	473	304	1258
PercentageTable Figure 3 - Footnote 2	76%	11%	31%	50%	24%	100%
Table Figure 3 - Footnote 1 Specimens from NWT, YT, and Nvt are sent to reference laboratories in other provinces. However, data on laboratory-confirmed detections of influenza from Nunavut are not currently available. Return to Table Figure 3 - Footnote 1 referrer Table Figure 3 - Footnote 2 Percentage of tests positive for sub-types of influenza A are a percentage of all influenza A detections. Return to Table Figure 3 - Footnote 2 referrer Table Figure 3 - Footnote 3 Unsubtyped: The specimen was typed as influenza A, but no result for subtyping was available. Return to Table Figure 3 - Footnote 3 referrer

Table 1 - Cumulative numbers of positive influenza specimens by type, subtype and age group reported through case-based laboratory reporting, Canada, weeks 2019-35 to 2019-47

Age groups (years)	Cumulative (August 25, 2019 to November 23, 2019)
	Influenza A				B	Influenza A and B
	A Total	A(H1N1)	A(H3N2)	A (Un subtyped)Table 1 Footnote 1	Total	#	%
0-4	93	21	29	43	38	131	13%
5-19	84	6	30	48	107	191	19%
20-44	137	20	42	75	90	227	22%
45-64	154	35	48	71	18	172	17%
65+	279	13	116	150	17	296	29%
Total	747	95	265	387	270	1,017	100%
Table 1 Footnote 1 Unsubtyped: The specimen was typed as influenza A, but no result for subtyping was available. Table 1 Return to footnote 1 referrer

Syndromic / Influenza-like Illness Surveillance

Healthcare Professionals Sentinel Syndromic Surveillance

In week 47, 1.6%, of visits to healthcare professionals were due to influenza-like illness (ILI) which is the average for this time of year (Figure 4).

Number of participants reporting in week 47: 81

The shaded area represents the maximum and minimum percentage of visits for ILI reported by week from seasons 2014-2015 to 2018-2019

Figure 4 - Text equivalent

Surveillance Week	2019-20	Average	Min	Max
35	0.6%	0.6%	0.4%	0.9%
36	0.4%	0.6%	0.4%	0.9%
37	0.7%	0.7%	0.5%	1.0%
38	1.1%	0.7%	0.6%	1.0%
39	0.8%	0.9%	0.5%	1.2%
40	1.0%	1.2%	0.8%	1.7%
41	0.9%	1.7%	0.8%	2.8%
42	1.1%	1.6%	1.2%	2.1%
43	0.7%	1.2%	0.8%	1.7%
44	0.9%	1.2%	0.7%	1.7%
45	0.8%	1.2%	0.9%	1.5%
46	1.3%	1.4%	1.2%	1.8%
47	1.6%	1.6%	1.1%	2.2%

FluWatchers

In week 47, 3,057 participants reported to FluWatchers, of which 1.5% (46) reported symptoms of cough and fever (Figure 5).

Among the 46 participants who reported cough and fever:

• 24% consulted a healthcare professional;
• 67% reported days missed from work or school, resulting in a combined total of 112 missed days of work or school.
• 62% reported having been vaccinated for influenza this season.

If you are interested in becoming a FluWatcher, sign up today.

Number of Participants Reporting in Week 47: 3,057

Figure 5 - Text equivalent

Surveillance Week	% cough and fever
40	2.2%
41	1.8%
42	1.7%
43	2.2%
44	1.6%
45	1.4%
46	1.2%
47	1.5%

Online Figure – Geographic distribution of FluWatchers participants reporting cough and fever, Canada, week 2019-47

Click on the map to access the link

Influenza Outbreak Surveillance

In week 47, three new outbreaks were reported: two in long term care facilities and one in a facility type categorized as ‘other’, which includes facilities such as private personal care homes, correctional facilities, and colleges/universities (Figure 6).

To date this season, a total of 23 laboratory-confirmed influenza outbreaks have been reported; thirteen in long-term care facilities, two in acute care facilities and eight in a facility type categorized as ‘other’. Of the outbreaks where influenza type was reported (21), eighteen were due to influenza A. Among the 11 outbreaks for which the influenza A subtype was reported, all were associated with A(H3N2). One ILI outbreak in a school/daycare has also been reported.

Number of provinces and territories reporting in week 47: 12 out of 13

Figure 6 - Text equivalent

Surveillance Week	Acute Care Facilities	Long Term Care Facilities	Other	Schools and Daycares	Remote and/or Isolated Communities
35	0	0	0	0	0
36	0	0	0	0	0
37	0	0	0	0	0
38	0	1	0	0	0
39	0	1	0	0	0
40	0	2	0	0	0
41	0	2	1	0	0
42	1	0	0	0	0
43	0	0	1	0	0
44	0	0	1	0	0
45	0	2	4	0	0
46	1	3	0	0	0
47	0	2	1	0	0

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

To date this season. 106 influenza-associated hospitalizations were reported by participating provinces and territories^{Footnote 1}.

• 85% of the cases were influenza A.
• Of the cases for which subtype was reported (78), 72% were associated with influenza A(H3N2).
• The greatest proportion of hospitalizations (42%) were among adults ≥ 65 years of age.

Thirteen ICU admissions and no deaths have been reported.

Number of provinces and territories reporting in week 47: 9 out of 9

Pediatric Influenza Hospitalizations and Deaths

In week 47, five pediatric (≤16 years of age) laboratory-confirmed influenza-associated hospitalizations were reported by the Immunization Monitoring Program Active (IMPACT) network (Figure 7). This is slightly below the average (13) for week 47 over the previous five seasons.

To date this season, 22 pediatric hospitalizations have been reported by the IMPACT network; 73% (16) cases were associated with influenza A and 27% (6) with influenza B. Among the six cases for which the influenza A subtype was reported, all were associated with A(H1N1).

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

Figure 7 - Text equivalent

Surveillance week	2019-2020	Average	Min	Max
35	0	0	0	1
36	2	0	0	1
37	0	1	0	2
38	0	1	0	2
39	1	1	0	3
40	0	1	0	2
41	2	1	0	3
42	2	2	0	5
43	3	5	2	12
44	1	5	1	15
45	1	10	2	37
46	6	13	1	41
47	5	13	2	36

Distribution of antigenic phenotype among characterized influenza viruses, Canada, weeks 2019-35 to 2019-47

Adult Influenza Hospitalizations and Deaths

Surveillance of laboratory-confirmed influenza-associated adult (≥16 years of age) hospitalizations by the Canadian Immunization Research Network (CIRN) Serious Outcomes Surveillance (SOS) network began on November 1st for the 2019-20 season. To date this season, five cases have been reported.

Influenza Strain Characterizations

From September 1 to November 28, 2019, the National Microbiology Laboratory (NML) has characterized 60 influenza viruses (30 A(H3N2), 17 A(H1N1) and 13 influenza B) that were received from Canadian laboratories.

Influenza A(H3N2)

Over recent years, circulating strains of A(H3N2) have evolved, and are increasingly difficult to characterize by hemagglutination inhibition (HI) assay. Genetic characterization is established by sequencing the hemagglutinin (HA) gene of the influenza viruses to compare their genetic properties.

Antigenic Characterization:

Among the eight influenza A(H3N2) viruses antigenically characterized to date, the majority (88%) showed reduced titer by HI assay to A Kansas/14/2017 using antiserum raised against egg-propagated A Kansas/14/2017 (Figure 8a).

Genetic Characterization:

Nearly all (97%) of the 30 A(H3N2) viruses genetically characterized this season belonged to genetic group 3C.2a1b based on sequence analysis of the HA gene. One virus belonged to the genetic group 3C.3a (Figure 9).

Group 3C.2a1b viruses analysed represent:

• 88% (7 out of 8) viruses that were also antigenically characterized.
• 100% (22 out of 22) viruses which did not grow to sufficient hemagglutination titer for antigenic characterization by HI assay.

A/Kansas/14/2017 belongs to genetic group 3C.3a and is the influenza A(H3N2) component of the 2019-20 Northern Hemisphere influenza vaccine.

Influenza A(H1N1)

Among the 17 A(H1N1) viruses characterized to date, all were antigenically similar to A/Brisbane/02/2018 by HI testing using antiserum raised against egg-propagated A/Brisbane/02/2018 (Figure 8b). A/Brisbane/02/2018 is the influenza A(H1N1) component of the 2019-20 Northern Hemisphere influenza vaccine.

Influenza B

Among the 13 influenza B viruses antigenically characterized this season, all belonged to the B/Victoria lineage, and the majority (62%) showed reduced titer by HI assay to B/Colorado/06/2017 using antiserum raised against cell culture-propagated B/Colorado/06/2017 (Figure 8c).

Sequence analysis showed that all of the eight viruses showing reduced titre had a three amino acid deletion (162-164) in the HA gene.

The recommended influenza B components for the 2019-20 Northern Hemisphere influenza vaccine are B/Colorado/06/2017 (Victoria lineage) and B/Phuket/3073/2013 (Yamagata lineage). B/Phuket/3073/2013 is included in the quadrivalent influenza vaccine.

Figure 8 - Text equivalent

A) A(H3N2) viruses - Number of viruses characterized: 8

Antigenic phenotype of A(H3N2) virus	Number of viruses	Percentage
A/Kansas/14/2017-like	1	13%
Reduced titer to A/Kansas/14/2017	7	88%

B) A(H1N1) viruses - Number of viruses characterized: 17

Antigenic phenotype of A(H1N1) virus	Number of viruses	Percentage
A/Brisbane/02/2018-like	17	100%
Reduced titer to A/Brisbane/02/2018	0	0%

C) B viruses -Number of viruses characterized: 13

Antigenic phenotype of influenza B virus	Number of viruses	Percentage
B/Colorado/06/2017-like	5	38%
Reduced titer to B/Colorado/06/2017	8	62%
B/Phuket/3073/2013-like	0	0%

Antiviral Resistance

The National Microbiology Laboratory (NML) also tests influenza viruses received from Canadian laboratories for antiviral resistance.

Oseltamivir:

60 influenza viruses (36 A(H3N2), 12 A(H1N1) and 12 B) were tested for resistance to oseltamivir:

• All influenza viruses tested were sensitive to oseltamivir.

Zanamivir:

60 influenza viruses (36 A(H3N2), 12 A(H1N1) and 12 B) were tested for resistance to zanamivir:

• All influenza viruses tested were sensitive to zanamivir.

Amantadine:

High levels of resistance to amantadine persist among influenza A(H1N1) and influenza A(H3N2) viruses. All viruses tested this season were resistant.

Vaccine Monitoring

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

Vaccine Coverage

Influenza vaccine coverage estimates for the 2019-20 season are anticipated to be available in February or March 2020.

Vaccine Effectiveness

Influenza vaccine effectiveness estimates for the 2019-20 season are anticipated to be available in February or March 2020.