FluWatch report: December 3 to December 9, 2023 (week 49)

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 surveillance links

Influenza/influenza-like illness activity - Geographic spread

In week 49, 24 regions across Canada reported sporadic influenza activity, 18 regions in seven provinces reported localized influenza activity (N.L., N.S., N.B., Ont., Sask., Alta., and B.C.), and five regions reported widespread activity (Alta. and B.C.) (Figure 1). The proportion of regions reporting influenza activity and the intensity of reported activity is increasing. One region in Canada reported no activity this week.

Number of Regions Reporting in week 49: 48 out of 53

Figure 1 - Text description

Province	Influenza Surveillance Region	Activity Level
N.L.	Eastern	Localized
N.L.	Labrador-Grenfell	No Activity
N.L.	Central	Localized
N.L.	Western	Sporadic
P.E.I.	Prince Edward Island	Sporadic
N.S.	Zone 1 - Western	Sporadic
N.S.	Zone 2 - Northern	Localized
N.S.	Zone 3 - Eastern	Sporadic
N.S.	Zone 4 - Central	Sporadic
N.B.	Region 1	Sporadic
N.B.	Region 2	Localized
N.B.	Region 3	Localized
N.B.	Region 4	Sporadic
N.B.	Region 5	Sporadic
N.B.	Region 6	Localized
N.B.	Region 7	Localized
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	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	Sporadic
Sask.	Central	Localized
Sask.	South	Localized
Alta.	North Zone	Widespread
Alta.	Edmonton	Widespread
Alta.	Central Zone	Widespread
Alta.	Calgary	Localized
Alta.	South Zone	Widespread
B.C.	Interior	Sporadic
B.C.	Fraser	Localized
B.C.	Vancouver Coastal	Widespread
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	Sporadic
Nvt.	Kivalliq	Sporadic
Nvt.	Kitimeot	Sporadic

Laboratory-confirmed influenza detections

The weekly percentage of tests positive for influenza (13.2% in week 49) continues to increase but is within expected levels for this time of year.

The following results were reported from sentinel laboratories across Canada in week 49 (Figures 2 and 3):

• A total of 4,323 laboratory detections (4,235 influenza A and 88 influenza B) were reported.
• Among subtyped influenza A detections (1,627), 89% (1,449) were influenza A(H1N1).
• Among detections for which age information was reported (3,581), 1,186 (33%) of detections were in individuals aged 0-19 years old. Across adult age groups, similar proportions are being observed: 23%: 20-44 years old, 21%: 45-64 years old, and 23%: 65+ years old.

To date this season (August 27, 2023 to December 9, 2023):

• 15,625 influenza detections were reported, of which 97% (15,209) were influenza A and among subtyped influenza A detections (7,252), influenza A(H1N1) accounted for 89% of detections.
• 13,415 laboratory-confirmed influenza detections with age information were reported, of which 4,497 (34%) were in individuals aged 0-19 years old. Across adult age groups, similar proportion are being observed: 23%: 20-44 years old, 22%: 45-64 years old, and 22%: 65+ years old (Figure 4).

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 49: 35 out of 35

Figure 2 - Text description

Surveillance Week	A(Unsubtyped)	A(H3N2)	A(H1N1)	Influenza B	Percent Positive A	Percent Positive B
35	19	26	51	9	0.7	0.1
36	12	11	50	9	0.4	0.1
37	28	14	46	6	0.5	0.0
38	28	15	57	4	0.5	0.0
39	18	11	74	20	0.5	0.1
40	39	20	80	13	0.6	0.1
41	43	10	50	7	0.5	0.0
42	59	15	96	19	0.7	0.1
43	99	29	136	23	1.2	0.1
44	291	53	312	25	2.6	0.1
45	683	52	461	37	4.7	0.1
46	1033	102	959	47	7.2	0.2
47	1157	119	1065	33	8.1	0.1
48	1704	155	1556	76	10.9	0.2
49	2320	178	1449	88	12.9	0.3

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.

The epidemic threshold is 5% tests positive for influenza. When it is exceeded, and a minimum of 15 weekly influenza detections are reported, a seasonal influenza epidemic is declared.

Figure 3 - Text description

Surveillance Week	Percentage of tests positive, 2023-2024	Percentage of tests positive, 2022-2023	Percentage of tests positive, 2021-2022	Maximum Percentage of Tests Positive	Minimum Percentage of Tests Positive	Average Percentage of Tests Positive
35	0.8	0.2	0.0	1.9	0.1	0.8
36	0.5	0.2	0.0	2.3	0.3	1.1
37	0.5	0.3	0.0	1.8	0.4	1.0
38	0.5	0.5	0.0	2.4	0.6	1.3
39	0.6	0.7	0.0	3.0	0.6	1.7
40	0.7	1.0	0.0	2.3	1.1	1.7
41	0.5	1.4	0.1	3.0	1.3	1.7
42	0.8	2.4	0.1	3.4	0.9	2.2
43	1.3	5.5	0.1	5.3	0.8	2.8
44	2.7	10.8	0.2	8.4	1.2	3.7
45	4.8	16.2	0.1	10.1	1.4	4.6
46	7.4	20.3	0.2	14.1	1.5	6.0
47	8.3	24.3	0.2	15.4	1.4	7.7
48	11.2	24.1	0.3	18.2	0.8	10.6
49	13.2	21.2	0.3	19.3	1.6	12.9
50	N/A	17.4	0.3	27.0	2.4	16.4
51	N/A	12.5	0.2	29.1	3.3	20.0
52	N/A	8.0	0.1	34.5	4.3	24.4
1	N/A	4.6	0.1	31.7	5.9	23.5
2	N/A	2.3	0.1	29.1	7.1	23.0
3	N/A	1.5	0.1	30.1	12.2	23.7
4	N/A	1.1	0.1	29.5	15.9	24.0
5	N/A	1.0	0.0	30.6	19.6	24.9
6	N/A	1.0	0.0	32.4	17.9	25.0
7	N/A	0.9	0.0	32.5	16.3	25.1
8	N/A	1.1	0.1	32.9	17.6	25.2
9	N/A	1.3	0.1	34.3	16.8	24.4
10	N/A	1.4	0.2	36.0	16.1	23.3
11	N/A	1.7	0.3	31.4	16.2	21.4
12	N/A	1.9	0.9	30.0	15.0	20.1
13	N/A	2.4	1.5	28.3	14.5	19.6
14	N/A	2.2	2.5	26.2	12.7	19.1
15	N/A	2.5	3.9	20.7	12.0	16.3
16	N/A	2.4	7.0	18.5	11.6	14.5
17	N/A	2.4	9.7	17.3	9.8	12.8
18	N/A	2.3	11.3	13.0	7.9	10.3
19	N/A	2.1	12.6	12.0	5.0	9.0
20	N/A	2.1	10.4	9.1	3.2	7.2
21	N/A	1.6	9.8	7.5	3.0	5.6
22	N/A	1.6	8.4	4.9	2.2	3.9
23	N/A	1.3	7.0	4.4	0.9	2.9
24	N/A	1.1	5.0	4.4	0.8	2.3
25	N/A	1.0	3.0	4.0	0.6	1.9
26	N/A	0.7	2.3	3.0	0.7	1.8
27	N/A	0.6	1.2	2.8	0.4	1.4
28	N/A	0.8	0.8	1.8	0.4	0.9
29	N/A	0.5	0.7	1.5	0.5	1.1
30	N/A	0.5	0.4	1.5	0.5	0.9
31	N/A	0.5	0.3	1.9	0.6	1.1
32	N/A	0.7	0.2	1.2	0.5	0.9
33	N/A	0.7	0.2	1.7	0.4	0.9
34	N/A	0.6	0.2	1.6	0.4	0.9

Laboratory data notes:

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

Due to different testing protocols of laboratories across Canada, some influenza A subtype detection counts may not be included in total influenza A detection counts and percent positivity calculations.

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	97.5%	2.5%	2068
5 to 19	95.4%	4.6%	2429
20 to 44	96.8%	3.2%	3019
45 to 64	98.9%	1.1%	2886
65+	98.9%	1.1%	3013

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	92.6%	7.4%	920
5 to 19	93.1%	6.9%	1100
20 to 44	88.3%	11.7%	1401
45 to 64	95.3%	4.7%	1351
65+	87.8%	12.2%	1372

Syndromic / influenza-like illness surveillance

Healthcare practitioners sentinel surveillance

In week 49, 2.1% of visits to healthcare professionals were due to influenza-like illness (ILI) (Figure 5). The percentage of visits for ILI is above expected levels for this time of year.

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 SARS-CoV-2, the virus that causes COVID-19. This makes the percentage of visits for ILI an important indicator of overall respiratory illness morbidity in the community in the presence of co-circulating viruses.

This indicator should be interpreted with caution as there have been a smaller number of sentinels reporting compared to previous seasons.

Number of Sentinels Reporting in Week 49: 40

The shaded area represents the maximum and minimum percentage of visits for ILI 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.

Figure 5 - Text description

Surveillance Week	2023-2024	2022-2023	2021-2022	Average	Min	Max
35	0.5%	0.6%	0.1%	0.6%	0.4%	0.9%
36	0.4%	1.2%	0.2%	0.6%	0.4%	0.9%
37	0.8%	0.6%	0.4%	0.7%	0.5%	1.0%
38	0.8%	0.9%	0.3%	0.7%	0.6%	1.0%
39	0.9%	1.0%	0.4%	0.9%	0.5%	1.2%
40	0.6%	0.5%	0.2%	1.2%	0.8%	1.7%
41	1.6%	1.1%	0.4%	1.7%	0.8%	2.8%
42	1.0%	1.2%	0.5%	1.6%	1.2%	2.1%
43	0.8%	0.9%	0.3%	1.2%	0.8%	1.7%
44	1.3%	0.6%	0.3%	1.2%	0.7%	1.7%
45	1.2%	1.0%	0.4%	1.2%	0.9%	1.5%
46	2.0%	0.9%	0.8%	1.4%	1.2%	1.8%
47	1.7%	0.7%	0.3%	1.6%	1.1%	2.2%
48	2.0%	1.1%	0.5%	1.5%	1.1%	2.2%
49	2.1%	0.9%	0.5%	1.7%	1.0%	2.8%
50	N/A	1.1%	0.4%	1.5%	1.1%	1.7%
51	N/A	1.7%	0.5%	1.9%	1.4%	2.7%
52	N/A	1.5%	0.5%	2.0%	1.0%	3.1%
1	N/A	2.1%	0.7%	3.4%	1.9%	5.4%
2	N/A	1.6%	0.4%	3.4%	1.8%	5.7%
3	N/A	1.4%	0.2%	2.3%	1.3%	3.7%
4	N/A	0.9%	0.3%	2.0%	1.1%	2.9%
5	N/A	1.0%	0.2%	2.1%	1.4%	3.1%
6	N/A	0.7%	0.5%	2.4%	1.4%	4.0%
7	N/A	0.7%	0.3%	2.4%	0.9%	3.5%
8	N/A	0.8%	0.2%	2.3%	0.8%	3.4%
9	N/A	0.7%	0.2%	2.3%	0.9%	3.1%
10	N/A	0.9%	0.2%	2.0%	1.0%	2.8%
11	N/A	0.6%	0.2%	1.9%	1.1%	2.8%
12	N/A	0.8%	0.3%	1.6%	0.6%	2.6%
13	N/A	1.2%	0.4%	1.6%	1.1%	2.6%
14	N/A	1.1%	0.2%	1.7%	1.1%	3.0%
15	N/A	1.2%	0.3%	1.3%	0.9%	1.9%
16	N/A	1.5%	0.3%	1.2%	0.8%	1.7%
17	N/A	1.3%	0.4%	1.2%	0.7%	1.7%
18	N/A	1.8%	0.5%	1.3%	0.5%	2.0%
19	N/A	1.7%	0.3%	0.9%	0.6%	1.3%
20	N/A	1.5%	0.5%	1.1%	0.6%	1.5%
21	N/A	1.4%	0.3%	0.9%	0.5%	1.3%
22	N/A	1.0%	0.3%	0.7%	0.3%	1.0%
23	N/A	1.1%	0.2%	0.8%	0.6%	1.0%
24	N/A	1.3%	0.2%	0.7%	0.6%	1.0%
25	N/A	1.0%	0.2%	0.6%	0.4%	0.8%
26	N/A	0.8%	0.2%	0.8%	0.5%	1.4%
27	N/A	1.7%	0.3%	0.6%	0.5%	0.7%
28	N/A	1.0%	0.1%	0.7%	0.5%	1.3%
29	N/A	0.9%	0.3%	0.9%	0.6%	1.7%
30	N/A	1.3%	0.2%	0.6%	0.2%	0.9%
31	N/A	0.9%	0.2%	0.4%	0.2%	0.6%
32	N/A	0.9%	0.2%	0.8%	0.3%	1.2%
33	N/A	0.8%	0.3%	0.7%	0.4%	1.3%
34	N/A	1.0%	0.5%	0.7%	0.4%	1.5%

FluWatchers

In week 49, 9,228 participants reported to FluWatchers, of which 2.2% reported symptoms of cough and fever (Figure 6). The percentage of FluWatchers reporting cough and fever has been increasing slightly but is within expected levels 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 SARS-CoV-2, the virus that causes COVID-19. This makes the proportion of individuals reporting cough and fever an important indicator of overall respiratory illness activity in the community in the presence of co-circulating viruses.

FluWatchers reporting is not impacted by changes in health services or health seeking behaviours.

Among the 202 participants who reported cough and fever:

• 23% consulted a healthcare professional.
• 80% reported days missed from work or school, resulting in an average of 2.9 missed days from work or school among those 162 participants.

Yukon had the highest participation rate this week (66 participants per 100,000 population) and the neighbourhood with postal code, K0A had the highest number of participants (127). 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 49: 9,228

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	2023-2024	2022-2023	2021-2022	Average	Min	Max
35	1.1%	1.3%	0.2%	N/A	N/A	N/A
36	1.2%	1.2%	0.3%	N/A	N/A	N/A
37	1.5%	1.6%	0.5%	N/A	N/A	N/A
38	2.0%	1.8%	0.5%	N/A	N/A	N/A
39	2.3%	2.3%	0.5%	N/A	N/A	N/A
40	1.8%	2.4%	0.6%	2.5%	2.2%	2.7%
41	1.6%	2.0%	0.5%	2.2%	1.8%	2.6%
42	1.7%	2.0%	0.4%	1.8%	1.6%	2.0%
43	1.7%	2.3%	0.5%	1.9%	1.5%	2.2%
44	1.9%	2.6%	0.5%	1.6%	1.4%	1.8%
45	1.9%	3.0%	0.5%	1.8%	1.4%	2.3%
46	1.9%	2.9%	0.4%	1.8%	1.2%	2.2%
47	2.0%	3.1%	0.6%	1.9%	1.4%	2.4%
48	2.2%	3.1%	0.5%	2.4%	1.7%	3.4%
49	2.2%	2.7%	0.4%	2.6%	2.0%	3.2%
50	N/A	2.1%	0.6%	2.9%	2.1%	3.8%
51	N/A	2.4%	1.0%	3.2%	2.5%	3.9%
52	N/A	2.1%	1.5%	4.0%	2.8%	5.4%
1	N/A	1.7%	1.1%	3.8%	2.9%	4.8%
2	N/A	1.3%	1.0%	2.9%	1.9%	3.9%
3	N/A	1.3%	0.8%	3.3%	2.3%	4.8%
4	N/A	1.2%	0.6%	3.1%	2.1%	4.2%
5	N/A	1.1%	0.6%	3.2%	2.6%	3.6%
6	N/A	1.4%	0.5%	3.5%	2.8%	4.3%
7	N/A	1.3%	0.4%	3.2%	2.6%	3.8%
8	N/A	1.3%	0.5%	3.1%	2.5%	3.6%
9	N/A	1.4%	0.5%	2.8%	2.4%	3.5%
10	N/A	1.5%	0.6%	2.6%	2.1%	3.1%
11	N/A	1.5%	0.9%	2.3%	1.9%	2.6%
12	N/A	1.3%	1.2%	2.6%	2.5%	2.8%
13	N/A	1.5%	1.8%	2.5%	2.0%	3.1%
14	N/A	1.3%	2.3%	2.1%	1.3%	2.6%
15	N/A	1.4%	1.9%	1.8%	1.6%	1.9%
16	N/A	1.2%	1.9%	2.0%	1.5%	2.4%
17	N/A	1.2%	1.6%	1.7%	1.4%	2.3%
18	N/A	1.1%	1.4%	1.5%	1.2%	2.1%
19	N/A	0.9%	1.3%	N/A	N/A	N/A
20	N/A	1.0%	1.2%	N/A	N/A	N/A
21	N/A	0.9%	1.2%	N/A	N/A	N/A
22	N/A	0.7%	1.2%	N/A	N/A	N/A
23	N/A	0.9%	1.2%	N/A	N/A	N/A
24	N/A	0.9%	1.3%	N/A	N/A	N/A
25	N/A	0.7%	1.3%	N/A	N/A	N/A
26	N/A	0.9%	1.8%	N/A	N/A	N/A
27	N/A	0.8%	2.0%	N/A	N/A	N/A
28	N/A	0.6%	1.9%	N/A	N/A	N/A
29	N/A	0.6%	1.8%	N/A	N/A	N/A
30	N/A	0.7%	1.6%	N/A	N/A	N/A
31	N/A	1.0%	1.3%	N/A	N/A	N/A
32	N/A	0.9%	1.2%	N/A	N/A	N/A
33	N/A	0.9%	1.4%	N/A	N/A	N/A
34	N/A	1.2%	1.3%	N/A	N/A	N/A

Influenza outbreak surveillance

In week 49, 39 laboratory-confirmed influenza outbreaks were reported.

To date this season (August 27, 2023 to December 9, 2023):

• 163 laboratory-confirmed influenza outbreaks have been reported
  • 71 were in LTC facilities (44%)
  • 42 were in a facility categorized as 'other' (26%)
  • 50 were in acute care facilities (31%)
  • All outbreaks were due to influenza A of which seven outbreaks were mixed with influenza B
  • Among outbreaks with subtyping information (74), influenza A(H1N1) was detected in 89% of the outbreaks
• 30 ILI outbreaks have been reported
  • All 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, COVID-19, or a mixture of viruses.

Number of provinces and territories^{Footnote 1} reporting in week 49: 12 out of 13

Figure 7 - Text description

Surveillance Week	Acute Care Facilities	Long Term Care Facilities	Other	Schools and Daycares	Remote and/or Isolated Communities
35	0	1	2	0	0
36	0	0	0	0	0
37	0	2	0	0	0
38	0	2	0	0	0
39	0	1	0	0	0
40	0	3	0	0	0
41	0	1	0	0	0
42	0	3	0	0	0
43	0	4	1	0	0
44	4	7	4	0	0
45	1	2	6	0	0
46	14	7	1	0	0
47	8	7	11	0	0
48	11	13	8	0	0
49	12	18	9	0	0

Influenza severe outcomes surveillance

Provincial/territorial influenza hospitalizations and deaths

In week 49, 243 influenza-associated hospitalizations, 35 ICU admissions, and less than five influenza-associated deaths were reported by participating provinces and territories^{Footnote 2}. Influenza hospitalizations are increasing week to week.

To date this season (August 27, 2023 to December 9, 2023), 1,241 influenza-associated hospitalizations were reported by participating provinces and territories:

• 98% of the hospitalizations were associated with influenza A.
• Of the cases with subtype information (1,034), 95% were associated with influenza A(H1N1).
• Adults aged 65 years of age and older accounted for 42% of reported hospitalizations. The highest cumulative hospitalization rates were among adults 65 years of age and older (36/100,000) and children under 5 years of age (31/100,000).

To date this season (August 27, 2023 to December 9, 2023), 152 ICU admissions and 38 influenza-associated deaths were reported.

Number of provinces and territories reporting in week 49: 8 out of 9

Figure 8 - Text description

Surveillance Week	0-4 yrs	5-19 yrs	20-44 yrs	45-64 yrs	65+ yrs	Overall
35	N/A	0.1	N/A	0.0	0.2	0.0
36	N/A	0.1	N/A	0.0	0.4	0.1
37	N/A	0.1	N/A	0.2	0.7	0.2
38	N/A	0.1	0.0	0.2	0.8	0.2
39	0.4	0.1	0.1	0.3	1.0	0.3
40	0.4	0.1	0.1	0.4	1.6	0.4
41	0.4	0.3	0.2	0.5	1.8	0.6
42	0.9	0.5	0.2	0.6	2.0	0.7
43	0.9	0.7	0.3	0.9	2.8	1.0
44	2.7	1.1	0.5	1.4	4.8	1.7
45	4.3	1.8	0.9	2.6	8.0	2.9
46	9.2	2.5	1.7	4.7	13.1	5.0
47	16.4	3.8	2.6	7.9	19.5	7.8
48	24.0	5.6	4.2	12.2	28.1	11.6
49	30.9	6.6	5.6	14.9	35.5	14.6

Pediatric influenza hospitalizations and deaths

Data from our pediatric sentinel network were not available for week 49.

Influenza strain characterization

Since September 1, 2023, the National Microbiology Laboratory Branch (NMLB) has characterized 232 influenza viruses (33 A(H3N2), 183 A(H1N1), and 16 influenza B) received from Canadian laboratories.

Antigenic Characterization

Changes in circulating influenza viruses are monitored by antigenic characterization. Antigenic characterization results show how similar the circulating viruses are to reference viruses. Reference viruses represent strains included in the current seasonal influenza vaccine.

Influenza A(H1N1)

A/Wisconsin/67/2022 is the influenza A(H1N1) component of the 2023-2024 Northern Hemisphere influenza vaccine.

• 182 H1N1 viruses were characterized as antigenically similar to A/Wisconsin/67/2022-like with antisera produced against cell-grown A/Wisconsin/67/2022.
• 1 influenza A(H1N1) showed reduced titer with antisera raised against cell-grown A/Wisconsin/67/2022.

Influenza A(H3N2)

A/Darwin/6/2021 (H3N2)-like virus is the influenza A(H3N2) component of the 2023-2024 Northern Hemisphere influenza vaccine.

• 31 influenza A(H3N2) were antigenically similar to A/Darwin/6/2021 (H3N2)-like virus using antisera raised against cell-grown A/Darwin/6/2021 (H3N2)-like virus.
• 2 influenza A(H3N2) showed reduced titer with antisera raised against cell-grown A/Darwin/6/2021 (H3N2)-like virus.

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 2023-2024 Northern Hemisphere influenza vaccine are B/Austria/1359417/2021 (Victoria lineage) and B/Phuket/3073/2013 (Yamagata lineage)

• 16 viruses characterized were antigenically similar to B/Austria/1359417/2021.

Genetic Characterization

Genetic characterization is used to determine how similar gene sequences of circulating influenza viruses are to the sequences of the vaccine components used in the current seasonal influenza vaccine.

Since September 1, 2023, NMLB has genetically characterized 161 influenza viruses.

Table 1: Genetic Characterizations results of influenza A(H3N2), influenza A(H1N1) and Influenza B, Canada, season 2023-2024

Virus Subtype or Lineage	HA Clade	Number of Viruses Characterized	HA Subclade	Number of viruses Characterized	HA genetic clades and subclades of the 2023-2024 Northern Hemisphere influenza vaccine components
A(H1N1)	6B.1A.5a	128	2a	32	The A(H1N1) component belongs to genetic clade 6B.1A.5a.2a.1
			2a.1	96
A(H3N2)	3C.2a1b.2a	23	2a.3a.1	23	The A(H3N2) component belongs to genetic clade 3C.2a1b.2a.2a
B/Victoria	V1A	10	3a.2	10	The B/Victoria component belongs to genetic clade V1A.3
B/Yamagata	Y3	0	Y3	0	The B/Yamagata component belongs to genetic clade Y3

Antiviral resistance

The National Microbiology Laboratory has not yet reported antiviral resistance results for influenza viruses collected during the 2023-2024 season.

Oseltamivir

228 influenza viruses (31 H3N2, 182 H1N1 and 15 influenza B) were tested for resistance to oseltamivir.

• All influenza viruses were sensitive to oseltamivir.

Zanamivir

229 influenza viruses (31 H3N2, 182 H1N1 and 16 influenza B) 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 vaccination coverage and vaccine effectiveness.

Vaccination coverage

Influenza vaccine coverage estimates for the 2023-2024 season are anticipated to be available in February or March 2024.

Vaccine effectiveness

Influenza vaccine effectiveness estimates for the 2023-2024 season are anticipated to be available in February or March 2024.

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.