Credit Canada’s FluWatch
Like in the United States, Canada is seeing sharply increased flu activity, and the vast majority of H3N2 viruses tested are falling into the `drifted’ category – making them a poor match to this year’s vaccine (see HAN Advisory On `Drifted’ H3N2 Seasonal Flu Virus).
Here then are some excepts from a much larger report:
- In week 50, laboratory detections of influenza increased sharply for the fourth consecutive week. The majority of laboratory detections continued to be reported in AB, ON and QC; but with increasing activity in SK, MB and NL.
- A(H3N2) continues to be the most common type of influenza affecting Canadians. In both laboratory detections and hospitalizations, the majority of cases have been among seniors ≥65 years of age.
- Similar to the previous week, there were a large number of newly-reported laboratory-confirmed outbreaks of influenza: 72 influenza A outbreaks in 8 provinces, of which 57 were in long-term care facilities (LTCF).
- To date, the NML has found that the majority H3N2 influenza specimens are not optimally matched to the vaccine strain which may result in reduced vaccine effectiveness against the H3N2 influenza virus. However, the vaccine can still provide some protection against H3N2 influenza illness and can offer protection against other influenza strains such as A(H1N1) and B.
Figure 2. Number of positive influenza tests and percentage of tests positive, by type, subtype and report week, Canada, 2014-15
Influenza Strain Characterizations
During the 2014-2015 influenza season, the National Microbiology Laboratory (NML) has characterized 30 influenza viruses [13 A(H3N2), 2 A(H1N1) and 15 influenza B]. When tested by hemagglutination inhibition (HI) assay, one influenza A (H3N2) virus was antigenically similar to A/Texas/50/2012, two influenza A (H1N1) viruses were antigenically similar to A/California/7/2009 and 12 influenza B viruses were antigenically similar to the B/Massachusetts/2/2012 (Yamagata lineage) recommended by the WHO for the 2014-15 seasonal influenza vaccine. Five influenza A(H3N2) viruses and three influenza B viruses showed reduced titers to antisera produced against strains recommended for the seasonal influenza vaccine. Seven of the 13 influenza A (H3N2) viruses were antigenically similar to the A/Switzerland/9715293/2013, which is the influenza A/H3N2 component recommended for the 2015 Southern Hemisphere influenza vaccine (Figure 4). Additionally, 58 A(H3N2) viruses were unable to be tested by HI assay; however, sequence analysis showed that 57 belonged to a genetic group that typically shows reduced titers to A/Texas/50/2012.
Figure 4. Influenza strain characterizations, Canada, 2014-2015, N = 30
Although the timing of the peak of flu season varies from year to year, often we see a big jump in numbers right after students return to their classrooms in the new year.
This week’s FluWatch also carries this statement regarding the outbreak of H5N2 in poultry in British Columbia:
Avian Influenza A(H5)
The Canadian Food Inspection Agency (CFIA) is continuing its investigation into an outbreak of highly pathogenic avian influenza H5N2 virus in British Columbia's Fraser Valley. To date, there have been ten infected premises. As part of regular investigation activities, CFIA is fully tracing movements in and out of these sites. This may lead to further premises being identified and depopulated, which would not be unexpected. While there are no reports of H5N2 related illness in humans, as a precautionary measure public health officials are monitoring workers who are exposed to affected poultry. Avian influenza viruses do not pose risks to food safety when poultry and poultry products are properly handled and cooked. Avian influenza rarely affects humans that do not have consistent contact with infected birds. Further information on the outbreak is provided on the following CFIA.