FluWatch report: June 14, 2020 to July 18, 2020 (weeks 25-29)  

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

During week 29, influenza/ILI activity was reported in only one region in BC (Figure 1).

Figure 1 - Text equivalent

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

Laboratory-Confirmed Influenza Detections

In weeks 25 to 29, the percentage of laboratory tests positive for influenza remained at the lowest level observed compared the past 9 seasons (Figure 2). The average percentage of tests positive for influenza during this 5-week period was 0.03% compared to 1.43% during the past 5 seasons.

In weeks 25-29, an average of 6,066 tests for influenza were performed at reporting laboratories, which is three times the average for this period over the past 5 seasons.

The percentage of positive tests crossed the seasonal threshold of 5% in week 12 (mid-March), indicating the end of the influenza season at the national level, 9 weeks earlier than average compared to the past 5 seasons. An abrupt end to the 2019-20 influenza season was observed in several countries, concurrent with the implementation of public health measures to reduce the spread of COVID-19.

Testing for influenza and other respiratory viruses has been influenced by the current COVID-19 pandemic. Changes in laboratory testing practices from March to June may affect the comparability of data to previous weeks or previous seasons.

To date this season (weeks 35 to 29), all influenza types and subtypes have circulated (Figure 3). Among the 55,364 laboratory detections of influenza reported:

• 59% (32,686) were influenza A.
• Among subtyped influenza A detections (7,332), A(H1N1) is the predominant subtype this season (68%).

Detailed information on age and type/subtype has been received for 42,538 laboratory-confirmed influenza cases (Table 1). To date this season (weeks 35 to 29):

• Cases of influenza A(H1N1) (3,739) were primarily in adults; 26% 20-44 years, 26% 45-64 years and 28% 65 years of age and older.
• Among cases of influenza A(H3N2) (2,057), the largest proportion of cases was in adults 65 years of age and older (46%).
• Cases of influenza B (18,193) were primarily in younger age groups; 22% under 5 years of age, 34% 5-19 years and 31% between 20 and 44 years of age.

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.

Number of Laboratories Reporting in Week 29: 32 out of 36

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.

Figure 2 - Text equivalent

Surveillance Week	A(Unsubtyped)	A(H3N2)	A(H1N1)	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	1620	261	431	1533	15.8	10.3
2	1690	165	493	1463	15.8	9.4
3	1575	139	417	1418	16.2	10.3
4	1727	133	370	1952	15.2	12.7
5	1983	97	440	2269	16.0	13.7
6	1970	75	344	2265	15.6	14.1
7	1741	76	321	1851	15.5	12.8
8	1768	74	255	1559	16.3	11.6
9	1928	58	303	1287	16.7	8.9
10	1772	81	399	1152	13.6	6.5
11	1552	70	354	1015	9.8	4.3
12	832	38	154	595	4.8	2.5
13	185	19	39	269	1.3	1.2
14	48	5	11	97	0.3	0.4
15	14	1	7	19	0.1	0.1
16	1	0	3	11	0.0	0.1
17	5	1	0	14	0.0	0.1
18	4	0	0	9	0.0	0.1
19	0	0	0	12	0.0	0.1
20	6	0	0	11	0.1	0.1
21	1	0	1	9	0.0	0.1
22	5	0	0	4	0.1	0.0
23	2	0	3	2	0.1	0.0
24	0	0	0	2	0.0	0.0
25	3	0	0	1	0.1	0.0
26	0	0	0	0	0	0
27	1	0	1	0	0	0
28	0	0	1	0	0	0
29	0	0	0	0	0	0

Figure 3 - Text equivalent

ProvincesTable Figure 3 - Footnote 1	Cumulative (August 25, 2019 to July 18, 2020)
	A Total	A(H1N1)	A(H3N2)	A(UnS)Table Figure 3 - Footnote 3	B Total	A & B Total
B.C.	4091	277	244	1852	2575	6666
Alta.	4374	1741	1287	1346	3417	7791
Sask.	1370	59	102	1209	700	2070
Man.	1648	174	134	1340	889	2537
Ont.	6513	2573	465	3475	2630	9143
Que.	12846	0	0	12846	10027	22873
N.B.	1047	61	29	957	1292	2339
N.S.	201	3	2	196	248	449
P.E.I.	144	0	0	144	78	222
N.L.	208	8	33	167	513	721
Y.T.	73	4	8	55	45	118
N.W.T	110	90	19	1	191	301
Nvt.	61	5	14	42	73	134
Canada	32686	4995	2337	23630	22678	55364
PercentageTable Figure 3 - Footnote 2	59%	15%	7%	72%	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 number of positive influenza specimens by type, subtype and age group reported through case-based laboratory reporting, Canada, weeks 2019-35 to 2020-29

Age groups (years)	Cumulative (August 25, 2019 to July 18, 2020)
	Influenza A				B	Influenza A and B
	A Total	A(H1N1)	A(H3N2)	A (Un subtyped) Table 1 Footnote 1	Total	#	%
0-4	3798	441	213	3144	4050	7849	18%
5-19	2745	298	261	2186	5992	8737	21%
20-44	5227	961	331	3935	5583	10810	25%
45-64	5033	983	304	3746	1160	6193	15%
65+	7542	1056	948	5538	1408	8950	21%
Total	24345	3739	2057	18549	18193	42538	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 weeks 25 to 29, an average of 0. 2% of visits to healthcare professionals were due to influenza-like illness (ILI) which continues to follow the downward trend observed since mid-March. In these five weeks, the proportion of visits for ILI was the lowest observed for this period compared to the past 5 seasons (Figure 4). This trend should be interpreted with caution as there have been changes in healthcare seeking behavior of individuals and a decreasing number of sentinels reporting in recent weeks. Given the evolving Canadian situation with COVID-19, we will continue to monitor this indicator closely.

Number of Sentinels Reporting in week 29: 54

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	2019-2020	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	1.1%	1.9%	1.4%	2.7%
52	2.5%	2.0%	1.0%	3.1%
1	2.9%	3.4%	1.9%	5.4%
2	1.5%	3.4%	1.8%	5.7%
3	1.8%	2.3%	1.3%	3.7%
4	1.4%	2.0%	1.1%	2.9%
5	1.5%	2.1%	1.4%	3.1%
6	1.7%	2.4%	1.4%	4.0%
7	1.3%	2.4%	0.9%	3.5%
8	1.4%	2.3%	0.8%	3.4%
9	1.3%	2.3%	0.9%	3.1%
10	1.4%	2.0%	1.0%	2.8%
11	1.7%	1.9%	1.1%	2.8%
12	0.9%	1.6%	0.6%	2.6%
13	0.9%	1.6%	1.1%	2.6%
14	0.7%	1.7%	1.1%	3.0%
15	1.0%	1.3%	0.9%	1.9%
16	0.6%	1.2%	0.8%	1.7%
17	0.5%	1.2%	0.7%	1.7%
18	0.5%	1.3%	0.5%	2.0%
19	0.3%	0.9%	0.6%	1.3%
20	0.5%	1.1%	0.6%	1.5%
21	0.3%	0.9%	0.5%	1.3%
22	0.4%	0.7%	0.3%	1.0%
23	0.2%	0.8%	0.6%	1.0%
24	0.2%	0.7%	0.6%	1.0%
25	0.2%	0.6%	0.4%	0.8%
26	0.1%	0.8%	0.5%	1.4%
27	0.2%	0.6%	0.5%	0.7%
28	0.3%	0.7%	0.5%	1.3%
29	0.2%	0.9%	0.6%	1.7%

FluWatchers

In week 29, 9,927 participants reported to FluWatchers. During weeks 25 to 29, the proportion of participants reporting symptoms of cough and fever was low at an average of 0.10% (Figure 5). The percentage of participants reporting cough and fever are at the lowest levels ever observed. This decline was concurrent with public health measures to reduce the spread of COVID-19, which coincides with the abrupt end of the influenza season at the national level. Given the ongoing Canadian response to the COVID-19 pandemic, monitoring of this indicator will continue throughout the summer.  

Among the 11 participants who reported cough and fever in week 29, 72% (8) consulted a healthcare professional

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

Number of participants reporting in week 29 : 9,927

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%
48	1.7%
49	2.2%
50	2.1%
51	2.6%
52	4.1%
1	4.3%
2	3.1%
3	3.3%
4	3.1%
5	3.4%
6	3.0%
7	2.7%
8	2.7%
9	2.4%
10	2.1%
11	2.5%
12	1.5%
13	0.9%
14	0.5%
15	0.3%
16	0.3%
17	0.2%
18	0.2%
19	0.3%
20	0.2%
21	0.1%
22	0.2%
23	0.1%
24	0.1%
25	0.1%
26	0.1%
27	0.1%
28	0.1%
29	0.1%

Online Figure - Geographic distribution of FluWatchers participants reporting cough and fever, Canada, week 2020-29

Click on the map to access the link

Influenza Outbreak Surveillance

In weeks 25 to 29, no outbreaks of influenza or influenza-like illness were reported (Figure 6).

To date this season, a total of 974 laboratory-confirmed influenza outbreaks have been reported; 64% (627) in long-term care facilities, 25% (244) in facilities categorized as ‘other’, 9% (88) in acute care facilities, and 2% (15) in schools/daycares. Of the 912 outbreaks where influenza type was reported, 87% (789) were due to influenza A. Among the 324 outbreaks for which the influenza A subtype was reported, 54% were associated with A(H1N1) and 46% with A(H3N2). To date this season, 176 ILI outbreaks have also been reported; 98% (173) in schools/daycares and 2% (3) in facilities categorized as ‘other’.

Number of provinces and territories reporting in week 29: 10 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	4	0	0	0
47	0	2	1	1	0
48	1	6	2	2	0
49	2	10	1	1	0
50	4	10	4	1	0
51	4	17	11	0	0
52	4	48	15	0	0
1	17	85	40	0	0
2	12	92	36	0	0
3	10	52	7	1	0
4	5	50	19	3	0
5	5	23	9	0	0
6	8	17	26	4	0
7	1	32	13	1	0
8	4	34	6	1	0
9	2	31	8	0	0
10	1	20	3	0	0
11	1	34	13	0	0
12	1	15	8	0	0
13	3	9	2	0	0
14	0	6	2	0	0
15	0	3	0	0	0
16	0	0	2	0	0
17	0	0	0	0	0
18	0	0	0	0	0
19	0	1	0	0	0
20	0	0	0	0	0
21	0	0	0	0	0
22	0	0	0	0	0
23	0	0	0	0	0
24	0	0	0	0	0
25	0	0	0	0	0
26	0	0	0	0	0
27	0	0	0	0	0
28	0	0	0	0	0
29	0	0	0	0	0

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

To date this season, 2,483 influenza-associated hospitalizations were reported by participating provinces and territories ^{Footnote 1}.

• 69% of the cases were associated with influenza A.
• Of the 1,098 cases for which subtype was reported, half were associated with influenza A(H3N2) and the other half were associated with A(H1N1).
• The highest cumulative hospitalization rates up to week 29 were among adults 65 years of age and older (78/100,000 population) and children under 5 years of age (75/100,000 population).

308 ICU admissions and 116 deaths have been reported.

• 70% of the ICU admissions and 73% of the deaths were associated with influenza A.

Number of provinces and territories reporting in week 29: 8 out of 9

Footnote 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.

Return to footnote 1 referrer

Figure 7 - Text equivalent

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	1.1
42	0.8	0.2	0.1	0.2	1.3
43	1.0	0.2	0.2	0.3	1.6
44	1.5	0.2	0.2	0.5	2.1
45	1.9	0.4	0.4	0.8	2.8
46	1.9	0.4	0.6	1.1	3.3
47	3.1	0.6	0.8	1.5	4.6
48	5.0	1.1	1.0	1.6	5.7
49	7.1	1.9	1.3	2.0	7.5
50	11.1	3.0	1.8	2.3	10.2
51	14.3	3.7	2.5	3.5	13.6
52	18.7	5.8	3.7	4.5	19.3
1	27.7	6.5	4.8	6.6	28.1
2	33.8	7.6	6.0	8.4	34.5
3	38.8	8.4	7.0	10.0	40.4
4	43.7	9.6	8.2	11.8	45.4
5	52.3	10.8	9.4	13.5	50.9
6	57.3	11.9	10.5	15.0	55.7
7	59.4	12.8	11.2	16.3	59.5
8	62.1	13.8	11.9	17.4	63.4
9	65.1	14.5	12.4	18.5	67.0
10	68.0	15.3	13.0	19.8	71.3
11	71.4	15.7	13.4	20.8	74.8
12	72.4	15.9	13.7	21.4	76.7
13	73.3	16.0	13.8	21.7	77.5
14	73.3	16.0	13.8	21.7	77.7
15	73.3	16.0	13.8	21.7	77.7
16	73.3	16.0	13.8	21.7	77.7
17	73.3	16.0	13.8	21.7	77.7
18	73.3	16.0	13.8	21.7	77.7
19	73.3	16.0	13.8	21.7	77.7
20	73.3	16.0	13.8	21.7	77.7
21	73.3	16.0	13.8	21.7	77.7
22	73.3	16.0	13.8	21.7	77.7
23	73.3	16.0	13.8	21.7	77.7
24	75.4	16.3	14.2	22.8	79.0
25	75.4	16.3	14.2	22.8	79.0
26	75.4	16.3	14.2	22.8	79.0
27	75.4	16.3	14.2	22.8	79.0
28	75.4	16.3	14.2	22.8	79.0
29	75.4	16.3	14.2	22.8	79.0

Pediatric Influenza Hospitalizations and Deaths

In weeks 25 to 29, less than five pediatric (≤16 years of age) laboratory-confirmed influenza-associated hospitalizations were reported by the Immunization Monitoring Program Active (IMPACT) network (Figure 8). Since the end of March, the weekly number of reported cases has been at the lowest level observed during this period over the past 5 seasons.

To date this season (weeks 35 to 29):

• 1,222 pediatric hospitalizations have been reported by the IMPACT network, of which 52% (631) were associated with influenza A and 48% (591) with influenza B.
• The largest proportion of hospitalizations (65%) were among children under 5 years of age (Figure 9).
• 209 ICU admissions were reported, of which 56% were associated with influenza A, and 81% were among children under 5 years of age.
• Seven pediatric deaths have been reported.

The shaded area represents the maximum and minimum number of cases reported by week from seasons 2014-15 to 2018-24

Figure 8 - 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	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	27	18	2	40
49	23	22	3	47
50	38	29	4	50
51	58	41	5	84
52	102	54	14	89
1	105	55	21	94
2	100	40	12	63
3	79	44	28	64
4	90	53	34	93
5	116	47	25	70
6	115	49	15	79
7	63	59	17	120
8	83	63	25	139
9	61	58	13	153
10	47	55	17	135
11	47	51	18	118
12	24	39	13	89
13	4	32	14	67
14	2	29	12	56
15	0	26	14	56
16	0	22	9	41
17	0	20	8	37
18	1	16	9	28
19	0	11	5	19
20	1	11	1	19
21	0	7	4	11
22	0	6	1	8
23	0	3	1	6
24	1	3	0	7
25	0	2	0	5
26	0	1	0	3
27	0	1	0	2
28	0	1	0	2
29	1	1	0	3

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 and ended  May 9^th for the 2019-20 season.

To date this season, 802 hospitalizations, 89 intensive care unit admissions, and 44 deaths have been reported (Figure 10).

• The majority of hospitalizations have been due to influenza A (78%), and among those subtyped (171) 92% were influenza A(H1N1).
• Among the 629 cases with influenza A, the largest proportion of hospitalizations were in adults 65 years of age and older (66%). Among the 170 cases with influenza B, 52% were in adults 65 years of age and older, and 26% of cases were between 16 and 34 years of age (Figure 11).
• 90% of hospitalized cases reported at least one type of comorbid condition.

Influenza Strain Characterizations

From September 1, 2019 to July 18, 2020, the National Microbiology Laboratory (NML) has characterized 12,21 influenza viruses (760 A(H1N1), 368 A(H3N2) and 893 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 109 influenza A(H3N2) viruses antigenically characterized to date, the majority (79%) showed reduced titer by HI assay to A Kansas/14/2017 using antiserum raised against egg-propagated A Kansas/14/2017. Twenty-three viruses were characterized as A Kansas/14/2017-like (Figure 12a).

Genetic Characterization:

Nearly all (96%) of the 368 A(H3N2) viruses genetically characterized this season belonged to genetic group 3C.2a1b based on sequence analysis of the HA gene. Fifteen viruses belonged to the genetic group 3C.3a (Figure 13).

Group 3C.2a1b viruses analysed represent:

• 86% (94 out of 109) viruses that were also antigenically characterized.
• 100% (259 out of 259) 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 760 A(H1N1) viruses characterized to date, 48% were antigenically similar to A/Brisbane/02/2018 by HI testing using antiserum raised against egg-propagated A/Brisbane/02/2018 (Figure 12b).

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

Influenza B

Antigenic Characterization:

Among the 184 influenza B viruses antigenically characterized this season, the vast majority (181) belonged to the B/Victoria lineage. Three viruses were antigenically characterized as similar to B/Phuket/3073/2013 (B/Yamagata lineage).

The majority (90%, 162) 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 12c).

Sequence analysis of 161 B/Victoria lineage viruses with reduced titre to B/Colorado/06/2017 showed that 100% had a three amino acid deletion (162-164) in the HA gene and belong to the genetic subclade V1A.3 (3Del). Sequencing is pending for the remaining viruses.

Genetic Characterization:

Genetic characterization was also performed on 481 B/Victoria lineage viruses. All of these viruses had a three amino acid deletion (162-164) in the HA gene and belong to the genetic subclade V1A.3 (3Del).

To date, 100% (709) of influenza B/Victoria viruses genetically characterized belong to the genetic subclade V1A.3 (3Del) (Fig 13b). Viruses in this genetic subclade are antigenically distinct from the vaccine strain B/Colorado/06/2017, which belongs to genetic subclade V1A.1 (2Del).

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. The vaccine strain B/Colorado/06/2017 belongs to genetic subclade V1A.1.

Antiviral Resistance

The National Microbiology Laboratory (NML) also tests influenza viruses received from Canadian laboratories for antiviral resistance. From September 1, 2019 to April 9, 2020, the following results were reported:

Oseltamivir:

733 influenza viruses (164 A(H3N2), 283 A(H1N1) and 286 B) were tested for resistance to oseltamivir:

• All influenza A(H3N2) and B viruses were sensitive to oseltamivir.
• Among the A(H1N1) viruses tested, 282 (99.6%) were sensitive to oseltamivir and one virus was resistant to oseltamivir with the H275Y mutation in the neuraminidase gene.

Zanamivir:

733 influenza viruses (164 A(H3N2), 283 A(H1N1) and 286 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

The Seasonal Influenza Immunization Coverage Survey is an annual telephone survey conducted between January and February that collects information from Canadians on whether they received the annual seasonal influenza vaccine that season. Vaccine coverage is measured as the percentage of people who received the influenza vaccine in a specific influenza season.

In the 2019-20 influenza season, coverage was similar to the 2018-19 season, at:

• 34% among adults aged 18 to 64 years.
  • 30% among adults aged 18-64 without chronic diseases.
  • 44% among adults aged 18 to 64 years with chronic diseases.
• 70% among seniors (aged 65 years and older).

Table 2 – Influenza vaccine coverage among adults (n=3,026)^{Table 2 - Footnote *} by age group gender^{Table 2 - Footnote ‡} and medical conditions^{Table 2 - Footnote †}, Seasonal Influenza Vaccination Coverage Survey, Canada, September 2019 – February 2020

Age group (years)	All		Male		Female
	N	Vaccine Coverage % (95% CI)	N	Vaccine Coverage % (95% CI)	N	Vaccine Coverage % (95% CI)
All adults (≥18)	3023	41.8 (39.7-43.9)	1320	37.2 (34.1-40.2)	1691	46.1 (43.2-49.0)
18-64	2234	34.1 (31.8-36.5)	1005	29.8 (26.5-33.1)	1218	38.4 (35.1-41.7)
with chronic diseases	668	43.6 (39.0-48.1)	268	38.3 (31.5-45.2)	397	47.9 (41.7-54.0)
without chronic diseases	1558	30.0 (27.3-32.7)	732	26.7 (22.9-30.5)	818	33.5 (29.6-37.3)
≥65	789	70.3 (66.7-73.8)	315	67.2 (61.5-72.9)	473	72.7 (68.3-77.1)
CI: 95% confidence interval Footnote * 3 people did not recall whether they had received the influenza vaccine and were excluded from coverage estimates. Return to table 2 footnote * referrer Footnote ‡ 4 people did not disclose their gender and 8 people did not identify themselves as male nor female. They were excluded from stratified analysis. Return to table 2 footnote ‡ referrer Footnote † 8 people who were 18-64 years old did not disclose whether they had any chronic medical conditions (CMC) and were excluded from stratified analysis. Return to table 2 footnote † referrer

Vaccine Effectiveness

The Canadian Sentinel Practitioner Surveillance Network (SPSN) provides estimates of the effectiveness of the seasonal influenza vaccine in preventing medically-attended illness due to laboratory-confirmed influenza among Canadians.

Based on data collected between November 1, 2019 and February 1, 2020, vaccine effectiveness (VE) was estimated to be 58% for any influenza, 44% for influenza A(H1N1), 62% for influenza A(H3N2), and 69% for influenza B. Substantial protection was observed among children 1 to 19 years of age against both influenza A and B. A good level of protection was also observed among working age adults (20-64 yrs) across all influenza types (Table 2). VE among adults 65 years and older, although imprecise due to small numbers, was lower at 18% (95% CI -59 to 58). The SPSN interim estimates are published and available online.

More information on the network and past VE findings can be viewed on the SPSN website.

Updated influenza vaccine effectiveness estimates will be published at the end of the 2019/2020 influenza season. At that time, sufficient data will likely be available to estimate VE by age-group, including adults 65 years and older with greater precision, as well as for influenza A subtypes.

Table 3 - Vaccine effectiveness estimates against medically-attended influenza illness, SPSN, November 1, 2019, to February 1, 2020

	All ages		1-19 years	20-64 years
	VE(%) (CI)Table 3 - Footnote *	N	VE(%) (CI)Table 3 - Footnote *	VE(%) (CI)Table 3 - Footnote *
All Influenza	58 (47, 66)	2808	74 (59, 84)	55 (41, 66)
Influenza A	49 (34, 60)	2128	70 (44, 84)	45 (25, 59)
Influenza A(H1N1)	44 (26, 58)	1948	-	-
Influenza A(H3N2)	62 (37, 77)	1561	-	-
Influenza B	69 (57, 77)	2080	77 (59, 87)	68 (51, 79)
Footnote * adjusted for age group, province, specimen collection interval and calendar time Return to table 2 footnote * referrer