FluWatch report: April 17, 2022 to May 7, 2022 (weeks 16-18)

On this page

• Influenza/Influenza-like Illness Activity - Geographic Spread
• Laboratory-Confirmed Influenza Detections
• Syndromic / Influenza-like Illness Surveillance
• Influenza Outbreak Surveillance
• Influenza Severe Outcomes Surveillance
• Influenza Strain Characterization
• Antiviral Resistance
• Influenza Vaccine Monitoring
• Provincial and International Influenza Reports

Influenza/Influenza-like Illness Activity - Geographic Spread

In week 18, 35 regions in twelve provinces and territories (B.C., Y.T., N.W.T., Alta., Sask., Man., Ont., Que., N.S., N.B.,P.E.I., N.L.) reported sporadic influenza/ILI activity and nine regions in four provinces (Alta., Ont., N.B., N.L.) reported localized influenza/ILI activity (Figure 1).

Number of Regions Reporting in Week 18: 50 out of 53

Figure 1 - Text description

Province	Influenza Surveillance Region	Activity Level
N.L.	Eastern	Sporadic
N.L.	Labrador-Grenfell	Localized
N.L.	Central	Sporadic
N.L.	Western	Sporadic
P.E.I.	Prince Edward Island	Sporadic
N.S.	Zone 1 - Western	No Activity
N.S.	Zone 2 - Northern	Sporadic
N.S.	Zone 3 - Eastern	Sporadic
N.S.	Zone 4 - Central	Sporadic
N.B.	Region 1	Localized
N.B.	Region 2	Localized
N.B.	Region 3	Localized
N.B.	Region 4	Sporadic
N.B.	Region 5	Localized
N.B.	Region 6	Localized
N.B.	Region 7	No Activity
Que.	Nord-est	Sporadic
Que.	Québec et Chaudieres-Appalaches	Sporadic
Que.	Centre-du-Québec	Sporadic
Que.	Montréal et Laval	Sporadic
Que.	Ouest-du-Québec	Sporadic
Que.	Montérégie	Sporadic
Ont.	Central East	Sporadic
Ont.	Central West	Sporadic
Ont.	Eastern	Sporadic
Ont.	North East	Sporadic
Ont.	North West	Sporadic
Ont.	South West	Localized
Ont.	Toronto	Localized
Man.	Northern Regional	No Activity
Man.	Prairie Mountain	No Activity
Man.	Interlake-Eastern	No Activity
Man.	Winnipeg	No Activity
Man.	Southern Health	Sporadic
Sask.	North	Sporadic
Sask.	Central	Sporadic
Sask.	South	Sporadic
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	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 weeks 16 to 18, 4,816 laboratory detections (4,810 influenza A and 6 influenza B) were reported. Detections of influenza have sharply increased since the beginning of April.

The weekly percentage of tests positive for influenza continues to increase and is now within pre-pandemic levels (11.6%). The percentage of tests positive for influenza recently exceeded the seasonal epidemic threshold of 5%, signaling the start of an influenza season. This increasing trend in laboratory detections is unusual because laboratory detections are typically decreasing at this time of year.

In weeks 16 to 18, a total of 49,532 tests for influenza were performed at reporting laboratories and the percentage of tests positive for influenza in week 18 was 11.6%. Compared to the past six pre-pandemic seasons (2014-2015 to 2019-2020), an average of 15,975 tests were performed for this time period, with an average of 10.3% of tests positive for influenza for week 18 (Figure 3).

To date this season (August 29, 2021 to May 7, 2022), 6,677 influenza detections (6,551 influenza A and 126 influenza B) have been reported, which is lower than what we have seen historically in the past six pre-pandemic seasons, where an average of 45,671 influenza detections were reported at this point in the season. Among subtyped influenza A detections (1,463), influenza A(H3N2) accounted for 98% of detections.

Detailed information on age and type/subtype has been received for 5,966 laboratory-confirmed influenza detections (Figure 4). Among the 5,966 detections, 2,919 (49%) were in individuals under 0-19 years old and 1,601 (27%) were in individuals 20-44 years old.

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

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 18: 32 out of 34

Due to different testing protocols of laboratories across Canada, differences exist in the number of detections included in various calculations, tables, and figures across products.

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 description

Surveillance Week	A(Unsubtyped)	A(H3N2)	A(H1N1)	Influenza B	Percent Positive A	Percent Positive B
35	3	0	0	0	0.0	0.0
36	1	0	0	0	0.0	0.0
37	1	3	0	0	0.0	0.0
38	0	0	0	0	0.0	0.0
39	0	0	1	0	0.0	0.0
40	0	0	0	2	0.0	0.0
41	2	1	0	3	0.0	0.0
42	0	1	1	2	0.0	0.0
43	2	1	0	3	0.0	0.0
44	1	2	0	16	0.1	0.1
45	2	9	0	10	0.1	0.1
46	3	8	0	9	0.1	0.1
47	4	11	0	12	0.1	0.1
48	11	7	0	28	0.2	0.2
49	29	6	0	9	0.2	0.1
50	19	12	1	4	0.2	0.0
51	25	12	1	6	0.2	0.0
52	10	12	1	2	0.1	0.0
1	10	11	1	1	0.1	0.0
2	16	2	2	3	0.1	0.0
3	4	2	0	2	0.0	0.0
4	4	2	0	0	0.1	0.0
5	4	1	0	1	0.0	0.0
6	2	1	0	1	0.0	0.0
7	1	1	0	0	0.0	0.0
8	5	2	1	2	0.1	0.0
9	8	6	2	0	0.1	0.0
10	7	11	0	0	0.2	0.0
11	18	9	0	1	0.3	0.0
12	46	36	3	0	0.9	0.0
13	121	106	1	0	1.5	0.0
14	217	152	0	1	2.5	0.0
15	346	199	0	2	3.8	0.0
16	850	258	4	2	7.0	0.0
17	1347	322	10	2	9.7	0.0
18	1682	226	2	2	11.6	0.0

The shaded area represents the maximum and minimum number of influenza tests or percentage of tests positive reported by week from seasons 2014-2015 to 2019-2020. Data from week 11 of the 2019-2020 season onwards are excluded from the historical comparison due to the COVID-19 pandemic.

Included in the cumulative detections this season are 11 co-infections of influenza A and B (total of 22 detections) that were suspected to be associated with live attenuated influenza vaccine (LAIV) receipt. Beginning in week 44 co-infections known or reported to be associated with recent LAIV were removed by the submitting laboratory or by the Public Health Agency of Canada as they do not represent community transmission of seasonal influenza viruses.

Figure 3 - Text description

a) Number of influenza tests, 2021-2022 compared to previous seasons

Surveillance Week	Number of Tests, 2021-2022	Number of Tests, 2020-2021	Maximum Number of Tests	Minimum Number of Tests	Average Number of Tests
35	7140	4996	1979	1311	1705
36	8012	5192	2208	1323	1707
37	9316	5335	2631	1778	2135
38	9821	6024	3039	1987	2502
39	9691	6707	3356	2365	2859
40	10776	7127	4078	2443	3134
41	10372	6817	4339	2673	3240
42	12508	6755	4649	2648	3526
43	13341	8227	4996	3084	3862
44	15442	9615	4966	2994	4020
45	17546	10748	5912	3117	4508
46	16418	11955	5589	3176	4564
47	16917	13103	6541	3587	5018
48	18531	18762	7416	3569	5645
49	19974	19649	8559	3836	6377
50	22543	16189	9464	4017	7155
51	28471	14059	11142	3487	8822
52	29555	12290	11338	4272	9184
1	28418	11681	14932	5371	12552
2	23659	14097	16104	5315	13289
3	19585	17002	15001	5270	11820
4	16496	15391	15414	5873	11441
5	15977	16607	16595	6739	11456
6	13873	12949	16121	8324	11339
7	13127	20727	14443	8074	10842
8	12180	21290	14024	7606	10865
9	11282	21891	14520	7507	10956
10	10752	20896	17681	7005	11084
11	10207	21220	12714	6435	9175
12	10808	23087	10431	5976	8238
13	11802	25811	9989	6063	7699
14	12697	26303	8830	4773	7046
15	13311	26284	7836	5090	6527
16	15505	26792	6826	5000	5890
17	17262	29154	6603	4440	5305
18	16765	22152	5640	4143	4780
19	-	12725	5480	3680	4311
20	-	9738	5097	3046	3862
21	-	7442	4001	2577	3197
22	-	6765	3790	2424	2944
23	-	6341	3257	1969	2591
24	-	5942	3120	2034	2449
25	-	5774	2659	1731	2148
26	-	5972	2600	1573	1988
27	-	5213	2163	1554	1833
28	-	4900	2223	1451	1857
29	-	5122	2256	1436	1796
30	-	5275	1950	1463	1664
31	-	5398	2022	1386	1671
32	-	4692	1928	1269	1574
33	-	5616	2089	1251	1671
34	-	5851	2098	1374	1698

b) Percentage of tests positive for influenza, 2021-2022 compared to previous seasons

Surveillance Week	Percentage of tests positive, 2021-2022	Percentage of tests positive, 2020-2021	Maximum Percentage of Tests Positive	Minimum Percentage of Tests Positive	Average Percentage of Tests Positive
35	0.04	0.02	1.87	0.11	0.82
36	0.01	0.00	2.28	0.30	1.13
37	0.03	0.00	1.78	0.40	0.99
38	0.00	0.02	2.35	0.55	1.30
39	0.01	0.00	2.95	0.67	1.71
40	0.02	0.00	2.33	1.08	1.70
41	0.06	0.01	3.02	1.32	1.72
42	0.05	0.00	3.40	0.87	2.18
43	0.05	0.01	5.32	0.84	2.83
44	0.20	0.07	8.55	1.20	3.70
45	0.13	0.04	10.10	1.39	4.63
46	0.15	0.03	14.11	1.51	6.05
47	0.19	0.07	15.36	1.44	7.71
48	0.34	0.05	18.20	0.84	10.61
49	0.28	0.04	19.71	1.64	13.01
50	0.25	0.01	27.02	2.36	16.82
51	0.20	0.01	29.09	3.30	20.11
52	0.10	0.00	34.54	4.28	24.48
1	0.08	0.00	31.66	5.85	23.41
2	0.12	0.00	29.10	7.06	23.01
3	0.05	0.01	30.07	12.24	23.63
4	0.05	0.00	29.45	15.89	23.96
5	0.04	0.00	30.62	19.60	24.90
6	0.05	0.02	32.39	17.89	25.00
7	0.02	0.01	32.51	16.28	25.05
8	0.08	0.00	32.87	17.45	25.14
9	0.12	0.00	34.28	16.80	24.59
10	0.16	0.00	35.99	16.05	23.22
11	0.28	0.01	31.41	16.19	21.41
12	0.86	0.00	30.03	15.03	20.10
13	1.52	0.00	28.25	14.50	19.56
14	2.48	0.00	23.16	12.66	17.86
15	3.84	0.01	20.73	11.95	16.27
16	6.96	0.00	18.52	11.64	14.48
17	9.71	0.00	17.30	9.76	12.83
18	11.63	0.00	13.02	7.88	10.26
19	-	0.00	11.95	4.96	8.98
20	-	0.01	9.13	3.19	7.22
21	-	0.01	7.45	2.97	5.60
22	-	0.00	4.96	2.19	3.86
23	-	0.00	4.39	0.87	2.86
24	-	0.02	4.36	0.81	2.25
25	-	0.00	3.95	0.63	1.88
26	-	0.00	3.08	0.69	1.81
27	-	0.00	2.83	0.42	1.48
28	-	0.00	1.84	0.41	0.91
29	-	0.00	1.55	0.47	1.09
30	-	0.04	1.46	0.46	0.90
31	-	0.00	1.93	0.58	1.11
32	-	0.00	1.19	0.52	0.92
33	-	0.00	1.69	0.40	0.85
34	-	0.02	1.57	0.42	0.92

Figure 4 - Text description

a) Proportion of influenza A and B by age-group

Age Group	Proportion of Influenza A	Proportion of Influenza B	Total Number Influenza Detections
0 to 4	97.2%	2.8%	1155
5 to 19	99.0%	1.0%	1714
20 to 44	98.3%	1.7%	1573
45 to 64	98.1%	1.9%	572
65+	98.6%	1.4%	851

b) Proportion of subtyped influenza A(H1N1) and A(H3N2) by age-group

Age Group	Proportion of A(H1N1)	Proportion of A(H3N2)	Total Number of Subtyped Influenza Detections
0 to 4	5.3%	94.7%	151
5 to 19	2.5%	97.5%	275
20 to 44	1.8%	98.2%	334
45 to 64	0.9%	99.1%	107
65+	1.1%	98.9%	188

Syndromic / Influenza-like Illness Surveillance

Healthcare Practitioners Sentinel Surveillance

In week 18, 2.1% of visits to healthcare professionals were due to influenza-like illness (ILI). The percentage visits for ILI in weeks 16-18 has been increasing since week 11 and has now exceeded pre-pandemic levels typical of this time of year.

Since the beginning of the surveillance season, the percentage of visits for ILI has been within or near expected pre-pandemic levels (Figure 5). ILI symptoms are not specific to any one respiratory pathogen and can be due to influenza, or other respiratory viruses, including respiratory syncytial virus and even SARS-CoV-2, the virus that causes COVID-19.

This indicator should be interpreted with caution as there have been changes in healthcare seeking behavior of individuals and a smaller number of sentinels reporting compared to previous seasons.

Number of Sentinels Reporting in Week 18: 47

The shaded area represents the maximum and minimum percentage of percentage of participants reporting cough and fever by week, from seasons 2014-2015 to 2019-2020. Data from week 11 of the 2019-2020 season onwards are excluded from the historical comparison due to the COVID-19 pandemic.

Figure 5 - Text description

Surveillance Week	2021-2022	2020-2021	Average	Min	Max
35	0.6%	0.1%	0.6%	0.4%	0.9%
36	1.2%	0.2%	0.6%	0.4%	0.9%
37	0.6%	0.4%	0.7%	0.5%	1.0%
38	0.9%	0.3%	0.7%	0.6%	1.0%
39	1.0%	0.4%	0.9%	0.5%	1.2%
40	0.5%	0.2%	1.2%	0.8%	1.7%
41	1.1%	0.4%	1.7%	0.8%	2.8%
42	1.2%	0.5%	1.6%	1.2%	2.1%
43	0.9%	0.3%	1.2%	0.8%	1.7%
44	0.6%	0.3%	1.2%	0.7%	1.7%
45	1.0%	0.4%	1.2%	0.9%	1.5%
46	0.9%	0.8%	1.4%	1.2%	1.8%
47	0.7%	0.3%	1.6%	1.1%	2.2%
48	1.1%	0.5%	1.5%	1.1%	2.2%
49	0.9%	0.5%	1.7%	1.0%	2.8%
50	1.1%	0.4%	1.5%	1.1%	1.7%
51	1.7%	0.5%	1.9%	1.4%	2.7%
52	1.5%	0.5%	2.0%	1.0%	3.1%
1	2.1%	0.7%	3.4%	1.9%	5.4%
2	1.6%	0.4%	3.4%	1.8%	5.7%
3	1.4%	0.2%	2.3%	1.3%	3.7%
4	0.9%	0.3%	2.0%	1.1%	2.9%
5	1.0%	0.2%	2.1%	1.4%	3.1%
6	0.7%	0.5%	2.4%	1.4%	4.0%
7	0.7%	0.3%	2.4%	0.9%	3.5%
8	0.8%	0.2%	2.3%	0.8%	3.4%
9	0.7%	0.2%	2.3%	0.9%	3.1%
10	0.9%	0.2%	2.0%	1.0%	2.8%
11	0.6%	0.2%	1.9%	1.1%	2.8%
12	0.8%	0.3%	1.6%	0.6%	2.6%
13	1.2%	0.4%	1.6%	1.1%	2.6%
14	1.1%	0.2%	1.7%	1.1%	3.0%
15	1.2%	0.3%	1.3%	0.9%	1.9%
16	1.5%	0.3%	1.2%	0.8%	1.7%
17	1.4%	0.4%	1.2%	0.7%	1.7%
18	2.1%	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	-	0.3%	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	-	0.2%	0.8%	0.5%	1.4%
27	-	0.3%	0.6%	0.5%	0.7%
28	-	0.1%	0.7%	0.5%	1.3%
29	-	0.3%	0.9%	0.6%	1.7%
30	-	0.2%	0.6%	0.2%	0.9%
31	-	0.2%	0.4%	0.2%	0.6%
32	-	0.2%	0.8%	0.3%	1.2%
33	-	0.3%	0.7%	0.4%	1.3%
34	-	0.5%	0.7%	0.4%	1.5%

FluWatchers

In week 18, 11,420 participants reported to FluWatchers, of which 1.4% reported symptoms of cough and fever (Figure 6). The percentage of FluWatchers who report cough and fever in weeks 16-18 has been at the highest level seen in the past two seasons and is within typical levels seen pre-pandemic for this time of year.

The reports of cough and fever are not specific to any one respiratory pathogen and can be due to influenza, or other respiratory viruses, including respiratory syncytial virus, rhinovirus, and even SARS-CoV-2, the virus that causes COVID-19. FluWatchers reporting is not impacted by changes in health services or health seeking behaviours.

Among the 160 participants who reported cough and fever:

• 56% consulted a healthcare professional;
• 81% reported days missed from work or school, resulting in a combined total of 129 missed days of work or school (average of 3.7 days);

The Northwest Territories had the highest participation rate this week (53 participants per 100,000 population) and the neighbourhood of K0A had the highest number of participants (142).  See what is happening in your neighbourhood! Downloadable datasets are also available on Open Maps.

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

Number of Participants Reporting in Week 18: 11, 420

The shaded area represents the maximum and minimum percentage of percentage of participants reporting cough and fever by week, from seasons 2014-2015 to 2019-2020. Data from week 11 of the 2019-2020 season onwards are excluded from the historical comparison due to the COVID-19 pandemic.

Figure 6 - Text description

Surveillance Week	2021-2022	2020-2021	Average	Min	Max
35	0.23%	0.22%	N/A	N/A	N/A
36	0.28%	0.21%	N/A	N/A	N/A
37	0.49%	0.38%	N/A	N/A	N/A
38	0.54%	0.29%	N/A	N/A	N/A
39	0.54%	0.45%	N/A	N/A	N/A
40	0.58%	0.49%	2.51%	2.18%	2.71%
41	0.46%	0.44%	2.18%	1.81%	2.57%
42	0.38%	0.33%	1.80%	1.61%	2.03%
43	0.53%	0.17%	1.87%	1.49%	2.18%
44	0.51%	0.26%	1.57%	1.39%	1.78%
45	0.54%	0.29%	1.83%	1.42%	2.32%
46	0.41%	0.28%	1.83%	1.22%	2.15%
47	0.57%	0.31%	1.93%	1.44%	2.39%
48	0.51%	0.26%	2.43%	1.67%	3.35%
49	0.40%	0.17%	2.56%	1.97%	3.16%
50	0.60%	0.15%	2.91%	2.12%	3.79%
51	1.03%	0.22%	3.18%	2.53%	3.95%
52	1.51%	0.10%	3.98%	2.81%	5.38%
1	1.08%	0.12%	3.84%	2.85%	4.76%
2	0.99%	0.21%	2.94%	1.90%	3.93%
3	0.77%	0.12%	3.25%	2.35%	4.84%
4	0.56%	0.12%	3.12%	2.13%	4.23%
5	0.64%	0.17%	3.19%	2.62%	3.59%
6	0.51%	0.11%	3.47%	2.76%	4.28%
7	0.43%	0.16%	3.18%	2.58%	3.79%
8	0.49%	0.06%	3.09%	2.54%	3.65%
9	0.45%	0.10%	2.81%	2.38%	3.53%
10	0.64%	0.18%	2.58%	2.12%	3.11%
11	0.88%	0.16%	2.33%	1.89%	2.63%
12	1.16%	0.17%	2.60%	2.46%	2.82%
13	1.79%	0.17%	2.48%	1.99%	3.06%
14	2.26%	0.19%	2.13%	1.35%	2.58%
15	1.95%	0.21%	1.78%	1.60%	1.93%
16	1.90%	0.14%	2.00%	1.47%	2.44%
17	-	0.22%	1.73%	1.40%	2.31%
18	-	0.15%	1.50%	1.19%	2.09%
19	-	0.14%	N/A	N/A	N/A
20	-	0.15%	N/A	N/A	N/A
21	-	0.09%	N/A	N/A	N/A
22	-	0.10%	N/A	N/A	N/A
23	-	0.08%	N/A	N/A	N/A
24	-	0.13%	N/A	N/A	N/A
25	-	0.12%	N/A	N/A	N/A
26	-	0.16%	N/A	N/A	N/A
27	-	0.11%	N/A	N/A	N/A
28	-	0.20%	N/A	N/A	N/A
29	-	0.20%	N/A	N/A	N/A
30	-	0.22%	N/A	N/A	N/A
31	-	0.21%	N/A	N/A	N/A
32	-	0.25%	N/A	N/A	N/A
33	-	0.31%	N/A	N/A	N/A
34	-	0.50%	N/A	N/A	N/A

Influenza Outbreak Surveillance

In weeks 16-18, 15 outbreaks were reported (seven in a long-term care facility, five in a facility categorized as ‘other’, which can include facilities such as private personal care homes, correctional facilities, and colleges/universities and three in remote or isolated communities).

To date this season (August 29, 2021 to May 7, 2022), 30 laboratory-confirmed influenza outbreaks and 83 ILI outbreaks have been reported. Among the 30 laboratory-confirmed influenza outbreaks, 13 were in long-term care facilities, 12 in facilities categorized as ‘other’, 3 in remote or isolated communities and 2 in an acute care facility.  All but one ILI outbreaks have been reported in schools and/or daycares.

Outbreaks of ILI are not specific to any one respiratory pathogen and can be due influenza, or other respiratory viruses, including respiratory syncytial virus, rhinovirus, and even COVID-19. Many respiratory viruses in addition to the flu commonly circulate during the fall and winter, and can cause clusters of cases with respiratory illness which could be captured as ILI. For more information on the respiratory viruses currently circulating in Canada, please refer to the Respiratory Virus Detections in Canada.

Number of provinces and territories^{Footnote 1} reporting in week 18: 12 out of 13

Influenza Severe Outcomes Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

In weeks 16-18, 187 influenza-associated hospitalizations and 20 ICU admissions were reported by participating provinces and territories^{Footnote 2}.

To date this season (August 29, 2021 to May 7, 2022), 249 influenza-associated hospitalizations were reported by participating provinces and territories.

• All but one hospitalization was due to influenza A.
• Of the cases for which subtype was reported (90), 100% were associated with influenza A(H3N2).
• The greatest proportion of hospitalizations  (41%) were in adults 65 years of age and older.

 22 influenza-associated ICU admissions were reported by participating provinces and territories.

Number of provinces and territories reporting in week 18: 9 out of 9

Pediatric Influenza Hospitalizations and Deaths

In week 18, 47 influenza-associated pediatric (≤16 years of age) hospitalizations were reported by the Immunization Monitoring Program Active (IMPACT) network. There has been in sharp increase in influenza-associated pediatric hospitalizations in recent weeks.

To date this season (August 29, 2021 to May 7, 2022), 125 pediatric influenza-associated hospitalizations have been reported, of which 79 (63%) were among children under the age of 5 years of age. Nine pediatric influenza-associated intensive care unit (ICU) admissions have been reported.

Adult Influenza Hospitalizations and Deaths

In week 18, less than five influenza-associated adult (≥16 years of age) hospitalizations were reported by the Canadian Immunization Research Network (CIRN) Serious Outcomes Surveillance (SOS) network.

To date this season (August 29, 2021 to May 7, 2022), 16 influenza-associated adult (≥16 years of age) hospitalizations have been reported by the CIRN SOS network.

Influenza Strain Characterization

To date this season (August 29, 2021 to May 7, 2022), the National Microbiology Laboratory (NML) has characterized 78 influenza viruses (76 A(H3N2), 2 A(H1N1)) received from Canadian laboratories.

Influenza A(H3N2)

Genetic Characterization

Among the 76 influenza A(H3N2) viruses genetically characterized, sequence analysis of the HA gene of these viruses showed that they all belonged to genetic group 3C.2a1b.2a2.

A/Cambodia/e0826360/2020 (H3N2)-like virus is the influenza A(H3N2) component of the 2021-2022 Northern Hemisphere seasonal influenza vaccine and belongs to genetic group 3C.2a1b.2a1.

A/Darwin/6/2021 (H3N2)-like virus is the influenza A(H3N2) component of the 2022 Southern Hemisphere seasonal influenza vaccine and belongs to the genetic group 3C.2a1b.2a2.

Antigenic Characterization

Among the 75 A(H3N2) viruses characterized:

• 13 viruses were antigenically similar to A/Cambodia/e0826360/2020 (H3N2)-like virus
• 62 showed reduced titers with antisera raised against egg-grown A/Cambodia/e0826360/2020 (H3N2)-like virus.

Influenza A(H1N1)

Antigenic Characterization

Among the two A(H1N1) viruses characterized:

• One H1N1 virus characterized was antigenically similar to A/Wisconsin/588/2019.
• One H1N1 showed reduced titer with ferret antisera raised against cell culture-propagated A/Wisconsin/588/2019.

A/Wisconsin/588/2019 is the influenza A(H1N1) component of the 2021-2022 Northern Hemisphere seasonal influenza vaccine.

Antiviral Resistance

The NML also tests influenza viruses received from Canadian laboratories for antiviral resistance.

Oseltamivir

77 influenza viruses (75 A(H3N2) and 2 A(H1N1)) were tested for resistance to oseltamivir:

• All influenza viruses were sensitive to oseltamivir.

Zanamivir

77 influenza viruses (75 A(H3N2) and 2 A(H1N1)) were tested for resistance to zanamivir:

• All influenza viruses were sensitive to zanamivir.

Influenza 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 reported receiving the influenza vaccine in a specific influenza season.
In the 2021-22 influenza season, coverage was similar to the 2020-21 season at:

• 30% among adults aged 18 to 64 years.
  • 27% among adults aged 18-64 without chronic medical conditions.
  • 38% among adults aged 18-64 with chronic medical conditions.
• 71% among seniors (aged 65 years and older).

Table 1 – Influenza vaccine coverage among adults (n=3,502)^{Footnote *} by risk group^{Footnote †} and gender^{Footnote ‡}, Seasonal Influenza Vaccination Coverage Survey, Canada, September 2021 – February 2022

Age group (years)	All		Male		Female
	N	Vaccine Coverage % (95% CI)	N	Vaccine Coverage % (95% CI)	N	Vaccine Coverage % (95% CI)
All adults (≥18)	3487	38.7 (36.9-40.6)	1548	33.4 (30.8-36.0)	1914	43.9 (41.3-46.5)
18-64	2389	30.1 (28.0-32.2)	1079	24.9 (22.1-27.8)	1286	35.0 (31.9-38.1)
with chronic medical conditions	713	37.6 (33.6-41.7)	298	37.0 (31.0-43.1)	407	38.3 (32.9-43.8)
without chronic medical conditions	1658	26.8 (24.4-29.2)	769	19.9 (16.9-23.0)	873	33.7 (29.9-37.4)
≥65	1098	71.0 (68.1-74.0)	469	67.0 (62.2-71.8)	628	74.6 (70.9-78.3)
Table 1 Note * 18 people did not recall whether they had received the influenza vaccine and were excluded from coverage estimates. Return to table 1 note * referrer Table 1 Note † 11 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 1 note † referrer Table 1 Note ‡ 11 people did not disclose their gender and 9 people did not identify as male or female. They were excluded from stratified analysis. Return to table 1 note ‡ referrer

Vaccine Effectiveness

Within season influenza vaccine effectiveness (VE) estimates are typically available in February or March of each year. Given the low influenza circulation this season to date, VE estimates will not be available for the 2021-2022 season.

Provincial and International Surveillance Links

See Influenza surveillance resources

Notes

The data in the FluWatch report represent surveillance data available at the time of writing. All data are preliminary and may change as updates 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.