FluWatch report: January 5 to 11, 2020 (week 02)

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Organization: Public Health Agency of Canada

Date published: 2020-01-17

Overall Summary

Influenza activity decreased across multiple indicators this week. This suggests that Canada may have reached peak influenza activity at the national level. Elevated activity is expected to continue in the coming weeks.
Influenza A(H3N2), A(H1N1) and B continue to co-circulate.
Influenza A remains the predominant circulating type and influenza B continues to circulate at higher levels than usual.
A(H1N1) and A(H3N2) are circulating in almost equal proportions. For the season to date, there is a slight majority (53%) of A(H1N1), due to an increase in detections in recent weeks.
The highest cumulative hospitalization rates are among children under 5 years of age and adults 65 years of age and older.

Influenza/ILI Activity (geographic spread)
Laboratory Confirmed Influenza Detections
Syndromic/Influenza-like Illness Surveillance
FluWatchers
Influenza Outbreak Surveillance
Severe Outcomes Influenza Surveillance
Influenza Strain Characterizations
Antiviral Resistance
Vaccine Monitoring
Provincial and International Influenza Reports

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

During week 02, 41 regions within 11 province/territories reported influenza activity; among these regions 44% reported sporadic activity, 46% reported localized activity, and 10% reported widespread activity (Figure 1).

Figure 1. Text equivalent follows. — **Figure 1 – Map of influenza/ILI activity by province and territory, Canada, week 2020-01**

Number of Regions Reporting in Week 02: 45 out of 53

Province	Influenza Surveillance Region	Activity Level
N.L.	Eastern	Sporadic
N.L.	Labrador-Grenfell	No Activity
N.L.	Central	Sporadic
N.L.	Western	Sporadic
P.E.I.	Prince Edward Island	Sporadic
N.S.	Zone 1 - Western	Localized
N.S.	Zone 2 - Northern	Sporadic
N.S.	Zone 3 - Eastern	No Activity
N.S.	Zone 4 - Central	Sporadic
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	Localized
Que.	Québec et Chaudieres-Appalaches	Widespread
Que.	Centre-du-Québec	Widespread
Que.	Montréal et Laval	Localized
Que.	Ouest-du-Québec	Widespread
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 Data
Man.	Prairie Mountain	No Data
Man.	Interlake-Eastern	No Data
Man.	Winnipeg	No Data
Man.	Southern Health	No Data
Sask.	North	Localized
Sask.	Central	No Activity
Sask.	South	No Activity
Alta.	North Zone	Localized
Alta.	Edmonton	Localized
Alta.	Central Zone	Localized
Alta.	Calgary	Localized
Alta.	South Zone	Sporadic
B.C.	Interior	Localized
B.C.	Fraser	Widespread
B.C.	Vancouver Coastal	Localized
B.C.	Vancouver Island	Sporadic
B.C.	Northern	Sporadic
Y.T.	Yukon	Sporadic
N.W.T.	North	Sporadic
N.W.T.	South	Sporadic
Nvt.	Qikiqtaaluk	No Data
Nvt.	Kivalliq	No Data
Nvt.	Kitimeot	No Data

Laboratory-Confirmed Influenza Detections

In week 02, the percentage of laboratory tests positive for influenza decreased slightly. Laboratory tests positive for influenza B declined but continue to be above average for this time of year. Among detections, the proportion that are influenza A continued to increase, and among subtyped influenza A detections, the proportion of A(H1N1) continued to increase.

The following results were reported from sentinel laboratories across Canada (Figures 2 and 3):

The percentage of tests positive for influenza decreased slightly from 26% in week 01 to 25% in week 02. While this is slightly higher than the average (23%) for week 02 over the past five seasons, the decline may suggest that we are near the peak of laboratory detections.
The percentage of tests positive for influenza A has been stable at approximately 15% since week 52.
The percentage of tests positive for influenza B declined for the second week in a row, from 13% in week 52 to 9% in week 02, but continues to be almost 5 times greater than the average (2.8%) for this time of year. The current level of circulation of influenza B is normally not observed until late March or early April.
The proportion of detections that were influenza A has increased in recent weeks, from 50% in week 51 to 63% in week 02.
Among subtyped influenza A detections, a mix of A(H1N1) and A(H3N2) continues to be detected. In week 02, the proportion of A(H1N1) increased from 62% in week 01 to 76%.

To date this season (weeks 35 to 02), 16,438 laboratory detections of influenza were reported:

59% (9,622) were influenza A.
Among subtyped influenza A detections (2,932), A(H1N1) is now the predominant subtype overall this season by a slight majority (53%), due to the increase in A(H1N1) detections in recent weeks.

Detailed information on age and type/subtype has been received for 12,168 laboratory-confirmed influenza cases (Table 1). To date this season (weeks 35 to 02):

Among cases of influenza A(H3N2) (1,204), the largest proportion were in adults 65 years of age and older (46%).
Cases of influenza B (5,508) were primarily in younger age groups; 55% of cases were under 20 years of age and 33% between 20 and 44 years of age.
Among cases of influenza A(H1N1) (911), nearly equal proportions of cases were in adults 20-44 years, 45-64 years, and 65 years of age and older (between 26 and 28% of cases were in each age-group).

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 2019-35 to 2020-02**

Number of Laboratories Reporting in Week 02: 35 out of 36

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	23	77	2.7	1.4
47	118	49	33	124	3.1	1.9
48	225	67	42	223	4.9	3.2
49	281	79	41	336	5.3	4.1
50	463	100	73	654	7.7	8.0
51	794	149	169	1094	10.6	10.4
52	1223	267	197	1439	15.0	12.7
1	1621	260	431	1533	15.8	10.3
2	1693	157	484	1438	15.8	9.3

Figure 3. Text equivalent follows. — **Figure 3 – Distribution of positive influenza specimens by type/subtype and province/territory^{Footnote *}, Canada, weeks 2019-35 to 2020-02**

Provinces^{Table Figure 3 - Footnote 1}	Cumulative (August 25, 2019 to January 11, 2020)
B.C.	743	141	225	134	486	1229
Alta.	1532	300	824	408	1855	3387
Sask.	147	0	0	147	36	183
Man.	337	46	52	239	483	820
Ont.	2674	1015	237	1422	610	3284
Que.	3946	0	0	3946	3134	7080
N.B.	118	19	7	92	152	270
N.S.	27	0	0	27	19	46
P.E.I.	8	0	0	8	11	19
N.L.	43	4	24	15	23	66
Y.T.	18	4	8	6	1	19
N.W.T	27	18	8	1	4	31
Nvt.	2	0	0	2	2	4
Canada	9622	1547	1385	6447	6816	16438
Percentage^{Table Figure 3 - Footnote 2}	59%	16%	14%	67%	41%	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 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 2020-01 to 2020-02
Age groups (years)	Cumulative (August 25, 2019 to January 11, 2020)
	Influenza A				B	Influenza A and B
	A Total	A(H1N1)	A(H3N2)	A (Un subtyped)^{Table 1 Footnote 1}	Total	#	%
0-4	939	102	124	713	1105	2044	17%
5-19	637	61	146	430	1930	2567	21%
20-44	1261	255	186	820	1792	3053	25%
45-64	1268	239	191	838	301	1569	13%
65+	2555	254	557	1744	380	2935	24%
Total	6660	911	1204	4545	5508	12168	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 02, 1.8% of visits to healthcare professionals were due to influenza-like illness (ILI) which is below the average for this time of year (Figure 4).

**Figure 4 – Percentage of visits for ILI reported by sentinels by report week, Canada, weeks 2019-35 to 2020-02**

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	0.7%	1.2%	0.9%	1.5%
46	1.1%	1.4%	1.2%	1.8%
47	1.2%	1.6%	1.1%	2.2%
48	0.9%	1.5%	1.1%	2.2%
49	1.0%	1.7%	1.0%	2.8%
50	1.4%	1.5%	1.1%	1.7%
51	1.2%	1.9%	1.4%	2.7%
52	2.6%	2.0%	1.0%	3.1%
1	3.0%	3.4%	1.9%	5.4%
2	1.8%	3.4%	1.8%	5.7%

FluWatchers

The proportion of FluWatchers participants reporting symptoms of cough and fever decreased in week 02 compared to the previous week. In week 02, 3,127 participants reported to FluWatchers, of which 3.0% (94) reported symptoms of cough and fever (Figure 5).

Among the 94 participants who reported cough and fever:

27% consulted a healthcare professional;
83% reported days missed from work or school, resulting in a combined total of 246 missed days of work or school.
71% reported having been vaccinated for influenza this season.

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

Figure 5. Text equivalent follows. — **Figure 5 - Percentage of participants reporting fever and cough, Canada, weeks 2019-40 to 2020-02**

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%
48	1.7%
49	2.2%
50	2.1%
51	2.6%
52	4.1%
1	4.3%
2	3.0%

Online Figure – Geographic distribution of FluWatchers participants reporting cough and fever, Canada, week 2020-02

Click on the map to access the link

Influenza Outbreak Surveillance

In week 02, the number of new laboratory-confirmed influenza outbreaks decreased. A total of 81 outbreaks were reported: 52 in long term care facilities, 8 in acute care facilities 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 336 laboratory-confirmed influenza outbreaks have been reported; 59% (200) in long-term care facilities, 27% (92) in facilities categorized as ‘other’, 12% (39) in acute care facilities, and 2% (5) in schools/daycares. Of the outbreaks where influenza type was reported (324), 91% (295) were due to influenza A. Among the 146 outbreaks for which the influenza A subtype was reported, 62% (91) were associated with A(H3N2). Four ILI outbreaks in schools/daycares have also been reported.

**Figure 6 – Number of new outbreaks of laboratory-confirmed influenza by report week, Canada, weeks 2019-35 to 2020-02**

Surveillance Week	Acute Care Facilities	Long Term Care Facilities	Other	Schools and Daycares
35	0	0	0	0
36	0	0	0	0
37	0	0	0	0
38	0	1	0	0
39	0	1	0	0
40	0	2	0	0
41	0	2	1	0
42	1	0	0	0
43	0	0	1	0
44	0	0	1	0
45	0	2	4	0
46	1	4	0	0
47	0	2	1	1
48	1	6	2	2
49	2	8	1	1
50	3	10	4	1
51	4	14	11	0
52	4	35	15	0
1	15	61	31	0
2	8	52	21	0

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

To date this season, 802 influenza-associated hospitalizations were reported by participating provinces and territories^{Footnote †}.

65% of the cases were associated with influenza A.
Of the cases for which subtype was reported (427), 78% were associated with influenza A(H3N2).
The highest cumulative hospitalization rates up to week 02 were among children under 5 years of age (27/100,000 population) and adults 65 years of age and older (26/100,000 population).

Eighty-one ICU admissions and thirteen deaths have been reported.

57% of the ICU admissions and 77% of the deaths were associated with influenza A.

**Figure 7 – Cumulative rates of influenza-associated hospitalizations by age-group and surveillance week, Canada, participating provinces and territories^{Footnote 1} weeks 2019-35 to 2020-02**

Surveillance Week	0-4 yrs	5-19 yrs	20-44 yrs	45-64 yrs	65+ yrs
35	0.0	0.0	0.0	0.0	0.0
36	0.0	0.0	0.0	0.0	0.2
37	0.0	0.0	0.0	0.1	0.2
38	0.0	0.0	0.0	0.1	0.4
39	0.2	0.0	0.0	0.1	0.6
40	0.2	0.0	0.0	0.1	0.8
41	0.4	0.2	0.1	0.2	1.0
42	0.8	0.2	0.1	0.2	1.3
43	1.0	0.2	0.2	0.3	1.5
44	1.5	0.2	0.2	0.5	2.0
45	1.9	0.4	0.4	0.8	2.7
46	1.9	0.4	0.6	1.1	3.3
47	3.1	0.6	0.8	1.5	4.5
48	5.0	1.1	1.0	1.6	5.6
49	7.1	1.9	1.3	1.9	7.5
50	11.1	3.0	1.8	2.2	10.0
51	14.5	3.7	2.5	3.4	13.4
52	19.1	5.5	3.6	4.5	19.0
1	25.0	5.9	4.1	5.6	24.3
2	26.7	6.4	4.4	6.0	26.1

Pediatric Influenza Hospitalizations and Deaths

In week 02, 99 pediatric (≤16 years of age) laboratory-confirmed influenza-associated hospitalizations were reported by the Immunization Monitoring Program Active (IMPACT) network (Figure 8). The weekly number of cases in this period above the 5-year maximum in week 02.

The sharp increase in the number of cases in recent weeks is likely due to the concurrent circulation of influenza A and B this season. The number of influenza A-associated pediatric hospitalizations is similar to the average for this time of year. Influenza B usually circulates later in the season, in February or March. However, this season, the number of hospitalizations with influenza B is well above average compared to previous seasons, and occurring earlier in the season.

To date this season (weeks 35 to 02) :

479 pediatric hospitalizations have been reported by the IMPACT network, of which 53% (254) were associated with influenza B and 47% (225) with influenza A.
The largest proportion of hospitalizations (65%) were among children under 5 years of age (Figure 9).
Among cases in children under 5 years of age (311), 53% of cases were associated with influenza A, compared to cases in children 5 to 16 years of age (168), among whom 64% of cases were associated with influenza B.
61 ICU admissions were reported, of which 52% (32) were associated with influenza A.
No pediatric deaths have been reported.

**Figure 8 – Number of pediatric (≤16 years of age) hospitalizations reported by the IMPACT network, by week, Canada, weeks 2019-35 to 2020-02**

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	1	5	2	12
44	2	5	1	15
45	3	10	2	37
46	6	13	1	41
47	6	13	2	36
48	26	18	2	40
49	23	22	3	47
50	39	29	4	50
51	59	41	5	84
52	98	54	14	89
1	110	55	21	94
2	99	40	12	63

**Figure 9 - Cumulative number of pediatric hospitalizations (≤16 years of age) with influenza by age-group reported by the IMPACT network, Canada, weeks 2020-01 to 2020-02**

Age Group	Total
0-5 mo	62
6-23 mo	126
2-4 yr	123
5-9 yr	104
10-16 yr	64

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. In week 02, the number of cases decreased compared to the previous week.

To date this season, 305 hospitalizations, 15 intensive care unit admissions, and less than five deaths have been reported (Figure 10). The majority of hospitalizations have been due to influenza A (88%), and among those subtyped (81) 89% were influenza A(H1N1). The largest proportion of hospitalizations are in adults 65-79 years of age (34%) and adults 80 years of age and older (32%) (Figure 11).

**Figure 10 - Number of adult hospitalizations (≥16 years of age) with influenza reported by the CIRN-SOS network, by week, Canada, weeks 2019-35 to 2020-02**

Surveillance Week	Number of Hospitalizations
35	No data
36	No data
37	No data
38	No data
39	No data
40	No data
41	No data
42	No data
43	No data
44	No data
45	No data
46	2
47	4
48	8
49	11
50	14
51	37
52	80
1	89
2	49

**Figure 11 - Cumulative numbers of adult hospitalizations (≥16 years of age) with influenza, by age-group, reported by the CIRN-SOS network, Canada, weeks 2019-35 to 2020-02**

Age Group	Total hospitalizations
16-34 yr	22
35-49 yr	28
50-64 yr	52
65-79 yr	105
80+ yr	98

Influenza Strain Characterizations

From September 1, 2019 to January 16, 2020, the National Microbiology Laboratory (NML) has characterized 384 influenza viruses (139 A(H3N2), 140 A(H1N1) and 105 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 35 influenza A(H3N2) viruses antigenically characterized to date, the majority (89%) showed reduced titer by HI assay to A Kansas/14/2017 using antiserum raised against egg-propagated A Kansas/14/2017. Four viruses were characterized as A Kansas/14/2017-like (Figure 12 a).

Genetic Characterization:

Nearly all (98%) of the 135 A(H3N2) viruses genetically characterized this season belonged to genetic group 3C.2a1b based on sequence analysis of the HA gene. Three viruses belonged to the genetic group 3C.3a (Figure 13).

Group 3C.2a1b viruses analysed represent:

89% (31 out of 35) viruses that were also antigenically characterized.
100% (104 out of 104) 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 140 A(H1N1) viruses characterized to date, 71% were antigenically similar to A/Brisbane/02/2018 by HI testing using antiserum raised against egg-propagated A/Brisbane/02/2018 (Figure 12 b).

A/Brisbane/02/2018 is the influenza A(H1N1) component of the 2019-20 Northern Hemisphere influenza vaccine.

Influenza B

Among the 105 influenza B viruses antigenically characterized this season, the vast majority (103) belonged to the B/Victoria lineage. Two viruses were antigenically characterized as similar to B/Phuket/3073/2013 (B/Yamagata lineage)..

The majority (87%) of B/Victoria lineage viruses showed reduced titer by HI assay to B/Colorado/06/2017 using antiserum raised against cell culture-propagated B/Colorado/06/2017 (Figure 12 c).

Sequence analysis showed that 100% (87) of the 90 B/Victoria lineage viruses showing reduced titre to B/Colorado/06/2017 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 12 - Distribution of antigenic phenotypes among characterized influenza viruses, Canada, September 1, 2019 to January 16, 2020**

A) Antigenic phenotypes among influenza A(H3N2) viruses
Number of viruses characterized: 35
A/Kansas/14/2017-like	4	11%
Reduced titer to A/Kansas/14/2017	31	89%

B) Antigenic phenotypes among influenza A(H1N1) viruses
Number of viruses characterized: 140
A/Brisbane/02/2018-like	99	71%
Reduced titer to A/Brisbane/02/2018	41	29%

C) Antigenic phenotypes among influenza B viruses
Number of viruses characterized: 105
B/Colorado/06/2017-like	13	12%
Reduced titer to B/Colorado/06/2017	90	86%
B/Phuket/3073/2013-like	2	2%

**Figure 13 - Distribution of genetic clades among characterized A(H3N2) influenza viruses, Canada, September 1, 2019 to January 16, 2020**

Number of viruses sequenced: 135
Subclade 3C.2a1b	132	98%
Clade 3C.3a	3	2%

Antiviral Resistance

The National Microbiology Laboratory (NML) also tests influenza viruses received from Canadian laboratories for antiviral resistance. From September 1, 2019 to January 16, 2020, the following results were reported:

Oseltamivir:

228 influenza viruses (104 A(H3N2), 52 A(H1N1) and 72 B) were tested for resistance to oseltamivir:

All influenza viruses tested were sensitive to oseltamivir.

Zanamivir:

228 influenza viruses (104 A(H3N2), 52 A(H1N1) and 72 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.

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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Date modified:: 2020-01-17

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