FluWatch report: March 31 to April 6, 2019 (Week 14)

Figure 1 - Text equivalent

Province	Influenza Surveillance Region	Activity Level
N.L.	Eastern	Localized
N.L.	Labrador-Grenfell	Sporadic
N.L.	Central	Localized
N.L.	Western	Localized
P.E.I.	Prince Edward Island	Localized
N.S.	Zone 1 - Western	Localized
N.S.	Zone 2 - Northern	Localized
N.S.	Zone 3 - Eastern	Localized
N.S.	Zone 4 - Central	Localized
N.B.	Region 1	Localized
N.B.	Region 2	Localized
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	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	Sporadic
Ont.	South West	Localized
Ont.	Toronto	Localized
Man.	Northern Regional	No Activity
Man.	Prairie Mountain	No Activity
Man.	Interlake-Eastern	Sporadic
Man.	Winnipeg	Sporadic
Man.	Southern Health	Sporadic
Sask.	North	Sporadic
Sask.	Central	Sporadic
Sask.	South	Sporadic
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	Sporadic
B.C.	Fraser	Sporadic
B.C.	Vancouver Coastal	Sporadic
B.C.	Vancouver Island	Sporadic
B.C.	Northern	Sporadic
Y.T.	Yukon	Localized
N.W.T.	North	Sporadic
N.W.T.	South	No Activity
Nvt.	Qikiqtaaluk	Sporadic
Nvt.	Kivalliq	No Activity
Nvt.	Kitimeot	No Activity

Laboratory-Confirmed Influenza Detections

In week 14, the following results were reported from sentinel laboratories across Canada (Figures 2 and 3):

• The percentage of tests positive for influenza was 19%; however, due to data quality issues this is likely an underestimate and should be interpreted with caution at this time.
• A total 1,243 laboratory detections of influenza were reported, of which 90% were influenza A.
• Influenza A(H3N2) accounted for 89% of subtyped influenza A detections.
• Since week 4 (mid-January), detections of influenza A(H3N2) have been steadily increasing.

To date this season, 42,104 laboratory-confirmed influenza detections have been reported:

• 97% have been influenza A.
• Among the 14,268 influenza A viruses subtyped, 77% have been A(H1N1)pdm09.
• Influenza B often circulates later in the season in Canada (Feb-Apr). Fewer influenza B detections have been reported this season compared to recent seasons at this time of year.

To date this season, detailed information on age and type/subtype has been received for 33,953 laboratory-confirmed influenza cases (Table 1):

• 83% of all influenza A(H1N1)pdm09 detections have been reported in individuals younger than 65 years of age.
• 57% of all influenza A(H3N2) detections have been reported in adults 65 years of age and older.

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.

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)pdm09	Influenza B
35	3	2	7	0
36	4	7	4	0
37	3	2	3	1
38	6	3	2	3
39	11	5	1	3
40	16	7	29	3
41	27	6	21	3
42	40	19	55	2
43	83	23	128	4
44	169	13	214	6
45	244	18	295	15
46	346	10	404	9
47	449	17	507	8
48	679	29	632	10
49	851	35	785	16
50	1368	35	828	14
51	1890	54	953	21
52	2292	55	903	26
1	2387	58	893	31
2	1985	93	1061	43
3	1613	101	585	40
4	1483	93	532	48
5	1449	112	433	43
6	1234	118	315	42
7	1116	128	244	33
8	1066	236	216	40
9	1172	285	213	64
10	1085	335	268	71
11	990	357	197	90
12	959	380	155	131
13	945	384	126	167
14	883	257	34	130

Figure 3 - Text equivalent

Reporting provincesTable Figure 3 - Footnote 1	Week (March 31 to April 6, 2019)					Cumulative (August 26, 2018 to April 6, 2019)
	Influenza A				B	Influenza A				B	A & B Total
	A Total	A (H1N1)pdm09	A (H3N2)	A(UnS)Table Figure 3 - Footnote 3	B Total	A Total	A (H1N1)pdm09	A (H3N2)	A(UnS)Table Figure 3 - Footnote 3	B Total
BC	0	0	0	0	0	5469	3016	1117	1336	146	5615
AB	157	8	106	43	22	6257	3581	659	2017	187	6444
SK	14	0	9	5	6	2295	1374	93	828	70	2365
MB	17	6	5	6	1	1075	302	52	721	19	1094
ON	217	12	120	85	6	5564	2033	1258	2273	143	5707
QC	432	0	0	432	35	15644	0	0	15644	395	16039
NB	73	0	0	73	50	2613	230	34	2349	132	2745
NS	42	0	0	42	2	709	0	0	709	13	722
PEI	8	2	6	0	0	263	219	43	1	0	263
NL	149	0	0	149	0	822	1	0	821	3	825
YT	11	3	7	1	0	92	53	11	28	0	92
N.W.T	1	1	0	0	0	172	170	2	0	1	173
NU	0	0	0	0	0	20	20	0	0	0	20
Canada	1121	32	253	836	122	40995	10999	3269	26727	1109	42104
PercentageTable Figure 3 - Footnote 2	90%	3%	23%	75%	10%	97%	27%	8%	65%	3%	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 first Table Figure 3 - Footnote 3 referrer Discrepancies in values in Figures 2 and 3 may be attributable to differing data sources. Cumulative data includes updates to previous weeks.

Table 1 – Cumulative numbers of positive influenza specimens by type, subtype and age-group reported through case-based laboratory reporting, Canada, weeks 2018-35 to 2019-14

Age groups (years)	Cumulative (August 26, 2018 to April 6, 2019)
	Influenza A				B	Influenza A and B
	A Total	A(H1N1) pdm09	A(H3N2)	A (UnS)Table 1 – Note 1	Total	#	%
0-4	6383	1667	163	4553	161	6544	19%
5-19	4764	1378	352	3034	242	5006	15%
20-44	6370	1957	442	3971	171	6541	19%
45-64	6466	1908	462	4096	86	6552	19%
65+	9117	1404	1902	5811	193	9310	27%
Total	33100	8314	3321	21465	853	33953	100%
Table 1 – Note 1 UnS: unsubtyped: The specimen was typed as influenza A, but no result for subtyping was available. Return to Table 1 – Note 1

Syndromic / Influenza-like Illness Surveillance

Healthcare Professionals Sentinel Syndromic Surveillance

In week 14, 1.1% of visits to healthcare professionals were due to influenza-like illness (ILI) (Figure 4).

The shaded area represents the maximum and minimum percentage of visits for ILI reported by week from seasons 2013-2014 to 2017-2018

Figure 4 - Text equivalent

Surveillance Week	2018-19	Average	Min	Max
35	0.6%	0.8%	0.5%	1.2%
36	0.7%	0.8%	0.7%	1.0%
37	0.6%	0.9%	0.7%	1.0%
38	0.5%	1.1%	1.0%	1.4%
39	1.8%	1.1%	0.9%	1.4%
40	0.6%	1.3%	0.9%	1.6%
41	1.1%	1.4%	0.9%	2.4%
42	1.0%	1.4%	1.0%	1.9%
43	0.9%	1.3%	1.0%	1.5%
44	0.8%	1.3%	0.9%	1.6%
45	1.3%	1.3%	1.2%	1.5%
46	1.3%	1.6%	1.0%	2.0%
47	1.3%	1.5%	1.1%	1.9%
48	1.5%	1.6%	0.8%	2.1%
49	1.6%	1.5%	1.0%	2.5%
50	1.5%	2.3%	1.3%	3.7%
51	1.0%	2.5%	1.6%	4.1%
52	3.2%	4.5%	1.7%	7.1%
1	2.8%	3.7%	1.7%	5.2%
2	1.8%	3.0%	1.1%	4.5%
3	1.1%	2.5%	1.3%	3.6%
4	1.3%	2.4%	1.7%	3.5%
5	1.4%	2.7%	2.0%	4.4%
6	0.9%	2.7%	2.1%	3.3%
7	0.8%	2.4%	1.7%	3.0%
8	0.9%	2.3%	1.9%	2.7%
9	1.0%	2.2%	1.8%	2.7%
10	1.1%	2.1%	1.8%	2.7%
11	0.5%	2.1%	1.7%	2.7%
12	1.1%	1.8%	1.1%	2.7%
13	1.2%	1.7%	1.2%	2.6%
14	1.1%	1.8%	1.3%	2.4%

Participatory Syndromic Surveillance

In week 14, 2,074 participants reported to FluWatchers, of which 48 (2.3%) reported symptoms of cough and fever (Figure 5).

Among the 48 participants who reported fever and cough:

• 25% consulted a healthcare professional;
• 83% reported days missed from work or school, resulting in a combined total of 111 missed days of work or school.

Figure 5 - Text equivalent

Surveillance Week	% cough and fever
40	2.6%
41	2.5%
42	1.7%
43	1.5%
44	1.3%
45	1.7%
46	2.0%
47	1.3%
48	2.4%
49	2.0%
50	3.7%
51	3.9%
52	3.6%
1	3.4%
2	2.8%
3	2.5%
4	2.9%
5	3.0%
6	2.6%
7	2.7%
8	2.5%
9	2.7%
10	3.1%
11	2.6%
12	2.4%
13	2.4%
14	2.3%

Influenza Outbreak Surveillance

In week 14, 18 new laboratory-confirmed influenza outbreaks were reported: long-term care facilities (LTCF) (13), acute care facilities (2) and other settings (3). Five new ILI outbreaks (LTCF (1), schools and daycares (3) and other settings (1)) were also reported in week 14. Among the outbreaks with available subtype information (6), all were associated with influenza A(H3N2).

To date this season, 706 laboratory-confirmed influenza outbreaks have been reported (Figure 6):

• 417 (59%) outbreaks were in LTCF, 30 were in schools and daycares, 105 in acute care facilities, and 154 were in other settings.
• Among the 633 outbreaks for which the influenza type was available, 97% (616) were associated with influenza A.
• Among the 271 outbreaks for which the influenza A subtype was available, 52% (141) were associated with influenza A(H3N2);

To date this season, 145 ILI outbreaks have been reported; 81 occurred in LTCF, 59 in schools, one in other settings and four in acute care facilities.

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	0	0	0	0
39	0	0	0	0	0
40	0	2	0	1	0
41	0	0	0	0	0
42	0	2	1	0	0
43	0	3	1	0	0
44	0	1	1	2	0
45	0	2	1	3	0
46	2	5	1	3	0
47	2	4	0	1	0
48	2	6	1	5	0
49	1	2	3	1	0
50	3	9	5	4	0
51	3	12	4	2	0
52	4	25	5	0	0
1	5	40	11	0	0
2	8	38	7	0	0
3	3	27	10	0	0
4	6	19	10	1	0
5	5	23	7	0	0
6	9	21	7	0	0
7	6	20	7	0	0
8	5	29	11	4	0
9	9	23	13	2	0
10	12	26	8	1	0
11	2	23	14	0	0
12	8	22	12	0	0
13	8	20	11	0	0
14	2	13	3	0	0

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

To date this season, 2,845 influenza-associated hospitalizations have been reported by participating provinces and territories^{Footnote 1}.

Hospitalizations (Table 2):

• 98.4% (2,798) were associated with influenza A
• Among the 1,643 cases for which the influenza subtype was available, 1,387 (84%) were associated with A(H1N1)pdm09.
• The highest estimated rate of hospitalization is among adults over 65 years of age.

Intensive Care Unit (ICU) cases and deaths:

• To date this season 508 ICU admissions and 147 deaths have been reported.
  • 42% (212) of reported ICU admissions were in adults aged 45-64 years.
  • All but five ICU admissions were associated with influenza A.
  • All but one of the deaths were associated with influenza A.

Table 2 – Cumulative number and estimated rate of hospitalizations by age-group reported by participating provinces and territories^{Footnote 1}, Canada, weeks 2018-35 to 2019-14

Age Groups (years)	Cumulative (August 26, 2018 to April 6, 2019)
	Influenza A	Influenza B	Rate per 100,000 population
0-4	378	17	82.99
5-19	225	15	17.30
20-44	338	5	12.06
45-64	732	4	33.82
65+	1125	6	92.96
Total	2798	47
%	98.3%	1.7%
Table 2 – Note 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. The cumulative rate of hospitalizations is calculated using the total population by age-group in participating provinces and territories. Return to Table 2 – Note 1

Pediatric Influenza Hospitalizations and Deaths

In week 14, 31 pediatric (≤16 years of age) hospitalizations with influenza have been reported by the Immunization Monitoring Program Active (IMPACT) network (Figure 7). Of the 31 hospitalizations, 21 (68%) were due to influenza A.

To date this season, 1,147 pediatric hospitalizations have been reported (Figure 8):

• 67% of cases were in children under 5 years of age.
• 96% (1,098) of cases have been associated with influenza A.
• Among the 335 cases for which the influenza subtype was available, 290 (87%) were associated with A(H1N1)pdm09.

To date this season, 203 ICU admissions, and 10 deaths have been reported.

• 60% (122) of ICU admissions were in children under 5 years of age.
• All but six of the ICU admissions have been associated with influenza A.
• 80% (8) of deaths occurred in children 2 to 4 years of age.
• All deaths have been associated with influenza A.

The shaded area represents the maximum and minimum number of cases reported by week from seasons 2010-11 to 2017-18

Figure 7 - Text equivalent

Surveillance week	2018-19	Average	Min	Max
35	0	0	0	0
36	0	0	0	1
37	0	0	0	2
38	0	0	0	2
39	0	1	0	3
40	0	0	0	2
41	1	1	0	2
42	5	1	0	4
43	12	1	0	3
44	15	3	1	6
45	37	3	2	4
46	41	5	1	13
47	36	4	0	9
48	40	9	2	23
49	46	15	3	28
50	51	23	4	47
51	83	32	4	72
52	89	47	7	92
1	90	40	5	75
2	62	35	4	62
3	70	38	4	67
4	60	35	7	47
5	49	40	11	59
6	47	38	15	79
7	43	40	17	120
8	43	47	25	139
9	35	50	13	153
10	46	48	17	135
11	42	41	18	118
12	42	33	13	89
13	31	32	14	67
14	31	24	12	56

Figure 8 - Text equivalent

Age Group	Total
0-5 mo	120
6-23 mo	296
2-4 yr	354
5-9 yr	252
10-16 yr	125

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 for the 2018-19 season.

To date this season, 847 hospitalizations, 103 ICU admissions and 46 deaths have been reported (Figure 9):

• 790 (93%) hospitalizations were associated with influenza A.
• A greater proportion of hospitalizations have been reported among  adults ≥65 years of age (59%) compared to adults <65 years of age (41%).
• Among the 182 cases for which the influenza subtype was available, 106 (58%) were associated with A(H1N1)pdm09.
• 88% of hospitalized cases reported more than one type of comorbid condition.  
• The most commonly reported comorbidity was endocrine disorders, which were reported in 95% of hospitalized cases.

Figure 9 - Text equivalent

Age Group	Total
20-34 yr	80
35-49 yr	79
50-64 yr	186
65-79 yr	247
80+ yr	255

Influenza Strain Characterizations

Since September 1, 2018, the National Microbiology Laboratory (NML) has characterized 1,904 influenza viruses (314 A(H3N2), 1,523 A(H1N1) and 67 B) that were received from Canadian laboratories.

Genetic Characterization of Influenza A(H3N2):

155 influenza A(H3N2) viruses did not grow to sufficient hemagglutination titer for antigenic characterization by hemagglutination inhibition (HI) assay. Therefore, NML has performed genetic characterization to determine the genetic group identity of these viruses.

Sequence analysis of the HA gene of the viruses showed that:

• 20 viruses belonged to genetic group 3C.2a.
• 131 viruses belonged to subclade 3C.2a1.
• Three viruses belonged to 3C.3a.
• One isolate could not be sequenced.

A/Singapore/INFIMH-16-0019/2016-like virus belongs to genetic group 3C.2a1 and is the influenza A(H3N2) component of the 2018-19 Northern Hemisphere influenza vaccine.

Antigenic Characterization:

Influenza A (H3N2):

• 103 influenza A(H3N2) viruses were antigenically characterized as A/Singapore/INFIMH-16-0019/2016-like by HI testing using antiserum raised against egg-propagated A/Singapore/INFIMH-16-0019/2016.
• 53 viruses showed reduced titer with ferret antisera raised against egg-propagated A/Singapore/INFIMH-16-0019/2016.
• A/Singapore/INFIMH-16-0019/2016-like virus is the influenza A(H3N2) component of the 2018-19 Northern Hemisphere influenza vaccine.
• 67 influenza A(H3N2) viruses characterized belonged to genetic group 3C.2a1. 17 viruses belonged to genetic group 3C.2a and 29 to 3C.3a. Sequencing is pending for the remaining isolates.

Influenza A(H1N1):

• 1,480 A(H1N1) viruses characterized were antigenically similar to A/Michigan/45/2015, which is the influenza A(H1N1) component of the 2018-19 Northern Hemisphere influenza vaccine.
• 43 viruses showed reduced titer with ferret antisera raised against cell culture-propagated A/Michigan/45/2015

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 2018-19 Northern Hemisphere influenza vaccine are B/Colorado/06/2017 (Victoria lineage) and B/Phuket/3073/2013 (Yamagata lineage).

• 16 influenza B viruses were characterized as B/Colorado/06/2017, which belong to the Victoria lineage and are included as an influenza B component of the 2018-19 Northern Hemisphere influenza vaccine.
• 28 viruses showed reduced titer with ferret antisera raised against cell culture-propagated B/Colorado/06/2017.
• 23 influenza B viruses were characterized as B/Phuket/3073/2013-like, which belongs to the Yamagata lineage and is included as an influenza B component of the 2018-19 Northern Hemisphere quadrivalent influenza vaccine.

Antiviral Resistance

Antiviral Resistance – Amantadine:

416 influenza A (73 A(H3N2) and 343 A(H1N1)) viruses were tested for resistance to amantadine and it was found that:

• All 416 influenza A viruses were resistant to amantadine.

Antiviral Resistance – Oseltamivir:

1,096 influenza viruses (112 A(H3N2), 933 A(H1N1) and 51 B) were tested for resistance to oseltamivir and it was found that:

• All 112 A(H3N2) viruses were sensitive to oseltamivir.
• Of the 933 A(H1N1) viruses tested, 929 were sensitive to oseltamivir and four viruses were resistant to oseltamivir with a H275Y mutation.
• All 51 B viruses were sensitive to oseltamivir.

Antiviral Resistance – Zanamivir:

1,095 influenza viruses (112 A(H3N2), 932 H1N1 and 51 B) were tested for resistance to zanamivir and it was found that:

• All 1,095 influenza viruses were sensitive to zanamivir.

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 related to the influenza vaccine in Canada. This survey measures vaccine coverage, which is the percentage of people who received the annual seasonal influenza vaccine in a specific influenza season.

In the 2018-19 influenza season, coverage was:

• 34% among adults aged 18 to 64 years.
  • 31% among adults aged 18-64 wihout chronic diseases.
  • 43% among adults aged 18 to 64 years with chronic diseases.
• 70% among seniors (aged 65 years and older).

Table 3 – Influenza vaccine coverage among adults (≥ 18 years of age) by age group, gender and chronic disease^{Table 3 – Note 1}, Seasonal Influenza Vaccination Coverage Survey, Canada, October 2018-February 2019

Age group (years)	Male		Female		Combined
	Total	Vaccine Coverage (%)	Total	Vaccine Coverage (%)	Total	Vaccine Coverage (%)
All adults (≥18)	1568	36.6	2150	46.8	3726	41.8
18-64	1252	28.6	1640	39.9	2898	34.3
without chronic diseases	948	25.8	1171	36.1	2124	30.8
with chronic diseases	304	36.3	465	48.5	770	42.8
≥65	316	69.0	510	70.9	828	69.9
Table 3 – Note 1 Excluded from stratified analysis: eight people who did not disclose their gender and four people (18-64 years old) who did disclose whether they had any chronic diseases. Return to Table 3 – Note 1

Vaccine Effectiveness

Vaccine effectiveness is a measure of how well the influenza vaccine is able to prevent influenza illness.  Throughout the season, surveillance networks monitor how well the influenza vaccine is working in the current season. Estimates can vary depending on several factors such as the study methods; the population, setting and outcomes that are being studied; the type and mix of vaccine products; the stage of the season and the kinds of influenza viruses that are circulating when the study is conducted.

Given an atypical late-season wave of influenza A(H3N2), the community-based Canadian Sentinel Practitioner Surveillance Network (SPSN) has undertaken an additional interim analysis to assess effectiveness of the 2018/19 influenza vaccine against A(H3N2) illness. The Canadian SPSN includes participation by sentinel practitioners in the four most populous provinces of Canada: Alberta, British Columbia, Ontario and Quebec.  Vaccine effectiveness (VE) monitoring methods are as described in prior publications, available at the SPSN website alongside historic and current VE findings.

Based on data collected as of March 30^th, 2019 including more than 2800 participants, the 2018/19 northern hemisphere vaccine has provided little or no protection against medically-attended outpatient A(H3N2) illness (VE of 23%; 95% CI: -9 to 46), including among working age adults 20-64 years old who comprise the majority of SPSN participants (VE of -16%; 95% CI: -76 to 23). Consistent with expected patterns, VE estimates for this delayed A(H3N2) wave are considerably lower than reported earlier by the SPSN for the primary A(H1N1)pmd09 epidemic based on data collected as of January 12^th, 2019. In that mid-season analysis, VE against A(H1N1)pdm09 was 72% (95% CI: 60 to 81) overall, with substantial protection observed in all age groups. In the most recent analysis spanning March 30^th, estimates against A(H1N1)pmd09 have remained stable at approximately 70%. The SPSN continues to monitor and will further update VE estimates at end of season.