FluWatch report: May 12 to May 18, 2019 (Week 20)

Influenza/Influenza-like Illness Activity (geographic spread)

During week 20, the following influenza activity levels were reported (Figure 1):

• 6 regions reported localized activity: in Man.(1), and Ont.(5).
• 25 regions reported sporadic activity: in B.C.(5), Sask.(3), Man.(3), Ont. (2), Que.(6), N.S.(1), N.B.(4), and P.E.I.(1).
• 13 regions in 6 different provinces and territories reported no activity.

Figure 1 - Text equivalent

Province	Influenza Surveillance Region	Activity Level
N.L.	Eastern	No data
N.L.	Labrador-Grenfell	No Data
N.L.	Central	No Data
N.L.	Western	No Data
P.E.I.	Prince Edward Island	Sporadic
N.S.	Zone 1 - Western	No Activity
N.S.	Zone 2 - Northern	No Activity
N.S.	Zone 3 - Eastern	No Activity
N.S.	Zone 4 - Central	Sporadic
N.B.	Region 1	Sporadic
N.B.	Region 2	Sporadic
N.B.	Region 3	Sporadic
N.B.	Region 4	No Activity
N.B.	Region 5	No Activity
N.B.	Region 6	Sporadic
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	Localized
Ont.	Central West	Localized
Ont.	Eastern	Localized
Ont.	North East	Localized
Ont.	North West	Sporadic
Ont.	South West	Sporadic
Ont.	Toronto	Localized
Man.	Northern Regional	Sporadic
Man.	Prairie Mountain	Sporadic
Man.	Interlake-Eastern	Sporadic
Man.	Winnipeg	Localized
Man.	Southern Health	No Activity
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	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 week 20, the following results were reported from sentinel laboratories across Canada (Figures 2 and 3):

• The percentage of tests positive for influenza decreased from 12% to 10% in week 20.
• A total of 469 laboratory detections of influenza were reported, of which 72% were influenza A.
• Influenza A(H3N2) accounted for 85% of subtyped influenza A detections.

To date this season, 47,622 laboratory-confirmed influenza detections have been reported:

• 96% have been influenza A.
• Among the 16,126 influenza A viruses subtyped, 70% have been A(H1N1)pdm09.
• Fewer influenza B detections have been reported this season compared to recent seasons at this time of year. The percentage of tests positive for influenza B in week 20 was similar to the previous week.

To date this season, detailed information on age and type/subtype has been received for 38,249 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.
• 58% 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.

Data for week 14 excludes subtyping results from one jurisdiction due to batch reporting of subtype information. The results for week 14 should be interpreted with caution.

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	939	387	128	167
14	1091	292	41	169
15	756	514	121	157
16	614	277	42	175
17	448	244	55	194
18	265	160	29	148
19	284	154	33	148
20	159	155	27	134

Figure 3 - Text equivalent

Reporting provincesTable Figure 3 - Footnote 1	Week (May 12 to May 18, 2019)					Cumulative (August 26, 2018 to May 18, 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	52	2	22	28	2	6342	3155	1551	1636	231	6573
AB	92	4	69	19	13	7033	3637	1206	2190	313	7346
SK	5	2	3	0	2	2397	1389	141	867	97	2494
MB	18	4	12	2	7	1170	327	115	728	57	1227
ON	60	6	45	9	10	6296	2085	1687	2524	244	6540
QC	93	0	0	93	68	17040	0	0	17040	798	17838
NB	14	9	2	3	22	2850	240	36	2574	322	3172
NS	0	0	0	0	1	784	0	0	784	19	803
PEI	0	0	0	0	1	278	221	56	1	2	280
NL	4	0	0	4	0	1029	1	0	1028	4	1033
YT	0	0	0	0	0	115	65	15	35	0	115
N.W.T	0	0	0	0	0	179	175	4	0	2	181
NU	0	0	0	0	0	20	20	0	0	0	20
Canada	338	27	153	158	131	45533	11315	4811	29407	2089	47622
PercentageTable Figure 3 - Footnote 2	72%	8%	45%	47%	28%	96%	25%	11%	65%	4%	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 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 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 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 2019-20

Age groups (years)	Cumulative (August 26, 2018 to May 18, 2019)
	Influenza A				B	Influenza A and B
	A Total	A(H1N1) pdm09	A(H3N2)	A (UnS)Table 1 – Note 1	Total	#	%
0-4	6739	1691	257	4791	306	7045	18%
5-19	5154	1392	484	3278	524	5678	15%
20-44	6885	2019	613	4253	337	7222	19%
45-64	7025	1973	668	4384	123	7148	19%
65+	10902	1485	2749	6668	254	11156	29%
Total	36705	8560	4771	23374	1544	38249	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 20, 0.8% 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	1.0%	1.8%	1.1%	2.7%
13	1.1%	1.7%	1.2%	2.6%
14	1.0%	1.8%	1.3%	2.4%
15	0.8%	1.6%	0.9%	1.9%
16	0.7%	1.5%	1.0%	1.9%
17	0.5%	1.5%	0.9%	2.2%
18	0.7%	1.2%	0.8%	1.6%
19	0.8%	1.3%	1.0%	1.7%
20	0.8%	1.2%	0.9%	1.4%

Participatory Syndromic Surveillance

FluWatchers surveillance has ended for the 2018-19 influenza season. On average 2,097 participants reported to FluWatchers each week, resulting in 64,672 questionnaires completed this season. The proportion of participants reporting fever and cough peaked in week 51 at 3.9% (Figure 5). Approximately 63% of FluWatchers participants reported being vaccinated for influenza in the 2018-19 season.

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%
15	1.8%
16	2.4%
17	2.3%
18	1.9%

Influenza Outbreak Surveillance

In week 20, three new laboratory-confirmed influenza outbreaks were reported: long-term care facilities (LTCF) (1) acute care facilities (1) and other settings (1). One new ILI outbreak was reported in a LTCF. All the influenza outbreaks were associated with influenza A.

To date this season, 848 laboratory-confirmed influenza outbreaks have been reported (Figure 6): 

• 504 (59%) outbreaks were in LTCF, 30 were in schools and daycares, 121 in acute care facilities, and 193 were in other settings.
• Among the 761 outbreaks for which the influenza type was available, 98% (743) were associated with influenza A.
• Among the 327 outbreaks for which the influenza A subtype was available, 60% (196) were associated with influenza A(H3N2);

To date this season, 160 ILI outbreaks have been reported; 94 occurred in LTCF, 61 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	6	24	6	0	0
6	9	23	7	0	0
7	6	20	7	0	0
8	5	30	11	4	0
9	9	23	14	2	0
10	12	27	8	1	0
11	4	24	14	0	0
12	9	22	15	0	0
13	9	23	11	0	0
14	3	22	6	0	0
15	6	19	8	0	0
16	0	15	10	0	0
17	1	12	8	0	0
18	1	14	4	0	0
19	1	8	2	0	0
20	1	1	1	0	0

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

To date this season, 3,097 influenza-associated hospitalizations have been reported by participating provinces and territories^{Footnote 1}. Note that data from one participating jurisdiction has not been available since surveillance week 13, so these figures are an underestimate of cases for this season.

Hospitalizations (Table 2):

• 97.6% (3,023) were associated with influenza A
• Among the 1,710 cases for which the influenza subtype was available, 1,415 (83%) 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 557 ICU admissions and 184 deaths have been reported.
  • 41% (227) of reported ICU admissions were in adults aged 45-64 years.
  • All but nine 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 2019-20

Age Groups (years)	Cumulative (August 26, 2018 to May 18, 2019)
	Influenza A	Influenza B	Rate per 100,000 population
0-4	395	23	87.82
5-19	235	20	18.38
20-44	355	10	12.83
45-64	777	7	36.03
65+	1261	14	104.79
Total	3023	74
%	97.6%	2.4%
Table 2 – Note 1 Influenza-associated hospitalizations are reported by N.L., P.E.I, N.S., N.B., Man., Alb., Y.T. and N.W.T. Only hospitalizations that require intensive medical care are reported by Sask. The cumulative rate of hospitalizations is calculated using the population by age-group in participating provinces and territories. Return to Table 2 – Note 1

Pediatric Influenza Hospitalizations and Deaths

To date this season, 1,298 pediatric hospitalizations have been reported (Figure 7 & 8):

• 66% of cases were in children under 5 years of age.
• 93% (1,201) of cases have been associated with influenza A.
• Among the 376 cases for which the influenza subtype was available, 305 (81%) were associated with A(H1N1)pdm09.

To date this season, 246 ICU admissions, and 10 deaths have been reported.

• 59% (148) of ICU admissions were in children under 5 years of age.
• All but 16 (94%) of the ICU admissions have been associated with influenza A; 83% of the 106 cases for which the influenza A subtype was available were associated with A(H1N1)pdm09.
• 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 2017-19

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	37	4	0	9
48	40	9	2	23
49	46	15	3	28
50	51	23	4	47
51	84	32	4	72
52	89	47	7	92
1	91	40	5	75
2	62	35	4	62
3	64	38	4	67
4	67	35	7	47
5	49	40	11	59
6	45	38	15	79
7	45	40	17	120
8	44	47	25	139
9	32	50	13	153
10	44	48	17	135
11	43	41	18	118
12	42	33	13	89
13	29	32	14	67
14	34	24	12	56
15	28	23	13	56
16	34	20	10	41
17	29	16	8	37
18	23	14	4	28
19	19	10	5	18
20	16	10	4	19

Figure 8 - Text equivalent

Age Group	Total
0-5 mo	138
6-23 mo	320
2-4 yr	400
5-9 yr	289
10-16 yr	151

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, 944 hospitalizations, 117 ICU admissions and 54 deaths have been reported (Figure 9):

• 873 (92%) hospitalizations were associated with influenza A.
• A greater proportion of hospitalizations have been reported among adults ≥65 years of age (60%) compared to adults <65 years of age (40%).
• Among the 207 cases for which the influenza subtype was available, 107 (52%) were associated with A(H1N1)pdm09.
• 87% of hospitalized cases reported more than one type of comorbid condition.
• The most commonly reported comorbidity was endocrine disorders, which were reported in 87% of hospitalized cases.

Figure 9 - Text equivalent

Age Group	Total
20-34 yr	92
35-49 yr	85
50-64 yr	198
65-79 yr	272
80+ yr	297

Influenza Strain Characterizations

From September 1, 2018 to 23 May, 2019, the National Microbiology Laboratory (NML) has characterized 2,252 influenza viruses (488 A(H3N2), 1,612 A(H1N1) and 152 B) that were received from Canadian laboratories.

Genetic Characterization of Influenza A(H3N2):

191 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.
• 168 viruses belonged to subclade 3C.2a1.
• Four 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):

• 162 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.
• 133 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.
• 101 influenza A(H3N2) viruses characterized belonged to genetic group 3C.2a1. 20 viruses belonged to genetic group 3C.2a and 116 to 3C.3a. Sequencing is pending for the remaining isolates.

Influenza A(H1N1):

• 1,569 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).

• 29 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.
• 100 viruses showed reduced titer with ferret antisera raised against cell culture-propagated B/Colorado/06/2017. Sequence analysis showed that 99 viruses that showed reduced titer had a three amino acid deletion (162-164) in the HA gene.
• 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:

449 influenza A (89 A(H3N2) and 360 A(H1N1)) viruses were tested for resistance to amantadine and it was found that:

• All 449 influenza A viruses were resistant to amantadine.

Antiviral Resistance – Oseltamivir:

1,287 influenza viruses (167 A(H3N2), 1,039 A(H1N1) and 81 B) were tested for resistance to oseltamivir and it was found that:

• All 167 A(H3N2) viruses were sensitive to oseltamivir.
• Of the 1,039 A(H1N1) viruses tested, 1,035 were sensitive to oseltamivir and four viruses were resistant to oseltamivir with a H275Y mutation.
• All 81 B viruses were sensitive to oseltamivir.

Antiviral Resistance – Zanamivir:

1,286 influenza viruses (167 A(H3N2), 1,038 H1N1 and 81 B) were tested for resistance to zanamivir and it was found that:

• All 1,286 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 (VE) is a measure of how well the influenza vaccine is able to prevent influenza illness. Throughout the influenza season, surveillance networks estimate how well the influenza vaccine is working. 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.

The community-based Canadian Sentinel Practitioner Surveillance Network (SPSN) published an interim VE estimate in January 2019 for A(H1N1)pdm09. Subsequently, given an atypical late-season wave of influenza A(H3N2),SPSN has undertaken an additional interim analysis to assess effectiveness of the 2018/19 influenza vaccine against medically-attended outpatient A(H3N2) illness. Vaccine effectiveness (VE) monitoring methods and results are available at the SPSN website.

Based on data collected as of March 30^th, 2019 from more than 2800 patients from B.C., Alta., Ont., and Que., the 2018/19 northern hemisphere vaccine effectiveness has varied depending on the strain.

• A(H1N1)pdm09: In the first interim 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 as of March 30th, estimates against A(H1N1)pmd09 have remained stable at approximately 70%.
• A(H3N2): In the most recent analysis, VE against A(H3N2) was 23% (95% CI: -9 to 46) overall. As the confidence interval crosses zero, this estimate does not provide evidence of vaccine protection against medically-attended outpatient A(H3N2) illness.

The SPSN continues to monitor and will further update VE estimates at end of season.