FluWatch report: February 28, 2021 to March 6, 2021 (week 09)

Influenza/influenza-like illness (ILI) activity (geographic spread)

During week 09, no influenza/ILI activity was reported (Figure 1).

Laboratory-confirmed influenza detections

In week 09, no laboratory detections of influenza were reported.

To date this season, 64 influenza detections have been reported (Figure 2), which is significantly lower than the past six seasons where an average of 38,355 influenza detections were reported for the season to date. All provinces and territories are closely monitoring indicators of influenza activity this season. Data in the FluWatch report represent surveillance data available at the time of writing, and may change as updates are received.

Thirty-one of the influenza detections reported to date this season are known to be associated with recent live attenuated influenza vaccine (LAIV) receipt and do not represent community circulation of seasonal influenza viruses. LAIV strains are attenuated but can be recovered by nasal swab in children and adults following vaccination with that product (i.e., "shedding"). For more information, please refer to the Canadian Immunization Guide Chapter on Influenza and Statement on Seasonal Influenza Vaccine for 2020–2021 (Section IV.2).

Overall, the percentage of laboratory tests positive for influenza remains at exceptionally low levels, despite the elevated levels of testing seen this week. In week 09, 19,477 tests for influenza were performed at reporting laboratories and the percentage of tests positive for influenza in week 09 was 0%. Compared to the past six seasons, the number of tests performed this week was higher than the average (10,956) and the percentage of tests positive for influenza remains well below average (24.6%) (Figure 3a and 3b). Over the past few weeks, influenza testing numbers have been fluctuating due to changes in provincial and territorial testing practices.

In Canada, at the national level, the influenza season typically starts around week 47 (mid-November) and is defined when at least 5% of influenza tests are positive and a minimum of 15 positive tests are observed nationally. Over the past 6 seasons, the influenza season has begun as early as week 43 (mid-October) and as late as week 1 (early January). As of week 09, influenza activity has remained below the threshold required to declare the start of the 2020-2021 influenza season.

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 Figure 2 or the Respiratory Virus Detections in Canada Report.

Syndromic / influenza-like illness surveillance

Healthcare practitioners sentinel syndromic surveillance

In week 09, 0.2% of visits to healthcare professionals were due to influenza-like illness (ILI), which remains lower than average compared to recent seasons (Figure 4).

This trend 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.

FluWatchers

In week 09, 12,109 participants reported to FluWatchers, and 22 participants (0.18%) reported symptoms of cough and fever (Figure 5). The percentage of participants reporting cough and fever remains at very low levels and may be a direct effect of individual and public health measures enacted to reduce the spread of COVID-19. FluWatchers reporting is not impacted by changes in health services or health seeking behaviours.

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Number of Participants Reporting in Week 09: 12,109

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

Figure 5 - Text equivalent

Surveillance Week	2020-2021	Average	Min	Max
35	0.22%	N/A	N/A	N/A
36	0.21%	N/A	N/A	N/A
37	0.38%	N/A	N/A	N/A
38	0.29%	N/A	N/A	N/A
39	0.45%	N/A	N/A	N/A
40	0.49%	2.51%	2.18%	2.71%
41	0.44%	2.18%	1.81%	2.57%
42	0.33%	1.80%	1.61%	2.03%
43	0.17%	1.87%	1.49%	2.18%
44	0.26%	1.57%	1.39%	1.78%
45	0.29%	1.83%	1.42%	2.32%
46	0.28%	1.83%	1.22%	2.15%
47	0.31%	1.93%	1.44%	2.39%
48	0.26%	2.43%	1.67%	3.35%
49	0.17%	2.56%	1.97%	3.16%
50	0.15%	2.91%	2.12%	3.79%
51	0.22%	3.18%	2.53%	3.95%
52	0.10%	3.98%	2.81%	5.38%
53	0.12%	3.91%	2.83%	5.07%
1	0.21%	3.84%	2.85%	4.76%
2	0.12%	2.94%	1.90%	3.93%
3	0.12%	3.25%	2.35%	4.84%
4	0.17%	3.12%	2.13%	4.23%
5	0.11%	3.19%	2.62%	3.59%
6	0.16%	3.47%	2.76%	4.28%
7	0.06%	3.18%	2.58%	3.79%
8	0.10%	3.09%	2.54%	3.65%
9	0.18%	2.81%	2.38%	3.53%
10	N/A	2.58%	2.12%	3.11%
11	N/A	2.33%	1.89%	2.63%
12	N/A	2.60%	2.46%	2.82%
13	N/A	2.48%	1.99%	3.06%
14	N/A	2.13%	1.35%	2.58%
15	N/A	1.78%	1.60%	1.93%
16	N/A	2.00%	1.47%	2.44%
17	N/A	1.73%	1.40%	2.31%
18	N/A	1.50%	1.19%	2.09%
19	N/A	N/A	N/A	N/A
20	N/A	N/A	N/A	N/A
21	N/A	N/A	N/A	N/A
22	N/A	N/A	N/A	N/A
23	N/A	N/A	N/A	N/A
24	N/A	N/A	N/A	N/A
25	N/A	N/A	N/A	N/A
26	N/A	N/A	N/A	N/A
27	N/A	N/A	N/A	N/A
28	N/A	N/A	N/A	N/A
29	N/A	N/A	N/A	N/A
30	N/A	N/A	N/A	N/A
31	N/A	N/A	N/A	N/A
32	N/A	N/A	N/A	N/A
33	N/A	N/A	N/A	N/A
34	N/A	N/A	N/A	N/A

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Influenza outbreak surveillance

In week 09, four influenza-like-illness (ILI) outbreaks in schools and/or daycares were reported.

To date this season, 121 influenza-like-illness (ILI) outbreaks in schools and/or daycares, and no other influenza or ILI outbreaks have been reported in any other settings.

Outbreaks of ILI in schools and daycares are identified when greater than 10% absenteeism due to ILI are reported in these settings. The number of ILI outbreaks in schools and daycares reported is higher compared to the same time period in the previous two seasons. This is not unexpected given changes to outbreak surveillance, specifically increased vigilance in schools to monitor and report absenteeism due to ILI, and the increased restrictions on attendance for children with symptoms of viral respiratory illness.

Outbreaks of ILI are not specific to any one respiratory pathogen and can be due influenza or other respiratory viruses, including rhinovirus and SARS-CoV-2, the virus that causes COVID-19. For more information on the respiratory viruses currently circulating in Canada, please refer to the Respiratory Virus Detections in Canada Report.

Number of provinces and territories reporting in week 09^{Footnote 1}: 11 out of 13

Severe outcomes influenza surveillance

Provincial/territorial influenza hospitalizations and deaths

In week 09, no influenza-associated hospitalizations were reported by participating provinces and territories^{Footnote 2}. To date this season no influenza-associated hospitalizations were reported by participating provinces and territories.

Number of provinces and territories reporting in week 09: 7 out of 9

Pediatric influenza hospitalization and deaths

In week 09, no influenza-associated hospitalizations were reported. To date this season, less than five pediatric (≤16 years of age) hospitalizations with influenza have been reported by the Immunization Monitoring Program Active (IMPACT) network.

Adult influenza hospitalization 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 has not begun for the 2020-2021 season.

Influenza strain characterizations

Due to the very low influenza circulation to date this season, the National Microbiology Laboratory has not received influenza viruses collected during the 2020-2021 season for strain characterization.

Antiviral resistance

Due to the very low influenza circulation to date this season, the National Microbiology Laboratory has not received influenza viruses collected during the 2020-2021 season for antiviral resistance testing.

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 2020-21 influenza season, coverage was similar to the 2019-20 season, at:

• 32% among adults aged 18 to 64 years.
  • 29% among adults aged 18-64 without chronic medical conditions.
  • 41% among adults aged 18 to 64 years with chronic medical conditions.
• 70% among seniors (aged 65 years and older).

Vaccine effectiveness

Influenza vaccine effectiveness 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 2020-2021 season.

Notes

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