Influenza has been M.I.A. across the northern hemisphere this winter, presumably because of the protective (physical distancing, masks and hygiene) measures being taken to prevent the spread of COVID-19.

That, and the fact that sizeable proportions of populations were vaccinated. In B.C. alone, health minister Adrian Dix said the province has distributed 2.2 million doses since last fall.

The BC Centre for Disease Control (BCCDC) monitors flu activity every year and in its latest report, it shows about 30,000 tests have been conducted to determine the prevalence of flu. Many of those tests are done at the same time as COVID-19 tests to determine the true culprit behind symptoms. Seven individuals have tested positive with various influenza strains. But each one of those individuals had been given a flu vaccine.

So does this mean that this year’s iteration of the flu vaccine has been a poor match? I delved into this.

Dr. Danuta Skowronski is a leading expert in influenza at BCCDC. She told me this:

“The live attenuated influenza vaccine (LAIV) which is given intra-nasally includes live virus that replicates but is attenuated (weakened) so as not to cause actual influenza infection,” she said, referring to the nasal spray product by AstraZeneca that is recommended for individuals aged two to 49. It’s a popular option for children since it’s a no-needles approach. Indeed, that suggests that a good proportion of the positive tests for flu were among children.

She went on to say:

“The nose swab that is collected to test for influenza viruses (is sensitive enough that it) would pick up these vaccine viruses in someone who recently received (the nasal spray).

The importance of all seven of the individuals in whom we found influenza viruses (including some with dual influenza virus detections) having recently received LAIV is that their viruses were likely LAIV viruses, NOT wild type circulating virus.

It is not that they were vaccinated and still got influenza virus infection. It is that they were recently vaccinated and their nose swabs picked up the vaccine strain.

The PCR test we do is very sensitive and can still pick up the LAIV strain. This is not unexpected.”

This is what the BCCDC says:

“As 2021 begins, influenza virus circulation remains remarkably absent in BC. Approximately 30,000 tests for influenza virus have been conducted in BC since the start of the 2020-21 season in week 40 (September 27, 2020) through to the end of the first week of 2021 (January 3-9, 2021).

So far, just 12 influenza viruses (7 influenza A and 5 influenza B) have been identified from among 7 individuals. However, each had recently received the live attenuated influenza vaccine (LAIV), suggesting vaccine-type rather than wild-type virus. Overall, there remains no indication of influenza virus circulation in BC. Elsewhere in the northern hemisphere, influenza virus detection also remains exceptionally low.

By contrast, for the same week 40 to week 1 period of the past 5 (2015-2019) seasons, there were on average 7,059 tests conducted and 1,005 influenza detections per season (range 285-1820). Average week 1 influenza positivity for the past 5 seasons was 32% (compared to zero percent positivity in week 1 of 2020-21).

No long-term care facility influenza outbreaks have been reported in 2020-21. Conversely, during the 2019-20 season, 19 long-term care facility outbreaks were reported between week 40 and week 1.”