The Extinction of Influenza

September 27, 2020

I just delivered a talk on influenza vaccination for the staff at Mount Alvernia Hospital. While preparing that talk, I wanted to provide up to date information on the epidemiology of influenza and how it was impacted by Covid-19. I was incredibly surprised with what I learnt.

The usual place to go to get up to date information is the WHO Influenza Update page. Last year, in September activity was more or less usual for this time of the year: the southern hemisphere was recovering from their winter peak activity and the northern hemispheric influenza did not start yet.

Similar WHO influenza update for September 2020 showed strikingly different results. Influenza activity was minimal in all regions of the world!

And we did not have influenza peak in the southern hemisphere!

I then turned to local Singapore data on MOH website and results were strikingly similar. The source is called Weekly Infectious Diseases Bulletin. The website provides more details for week 38 (13-19 September 2020).

Polyclinic attendances for the acute respiratory tract infections were at historical low.

And according to Bulletin: “The overall positivity rate for influenza among Influenza Like Illness (ILI) samples (n=220) in the community was 0.0% in the past 4 weeks. There were no Influenza positive surveillance samples in Aug 2020.”

Basically, we did not detect single case of influenza among polyclinic patients with acute respiratory infections! That is an astonishing finding!

What happened? There are several possible explanations:

  1. First of all the measures implemented to control the spread of the Covid-19 would also have impact on the spread of influenza. Universal mask wearing, border closures, social distancing measures decreased the spread of influenza.
  2. Health seeking behavior changed. Perhaps some people with minor respiratory infections decide not to see doctor in order to avoid Covid-19 testing and prolonged MC?
  3. Globally, some countries overburdened with Covid may have no resources to conduct influenza surveillance.

I am sure that there are many more possible explanations. Nevertheless, the disappearance of influenza is truly astonishing!

References:

  1. WHO Influenza Update page: https://www.who.int/influenza/surveillance_monitoring/updates/en/
  2. WHO Influenza Update – September 2019: https://www.who.int/influenza/surveillance_monitoring/updates/2019_09_16_surveillance_update_350.pdf?ua=1
  3. WHO Influenza Update – September 2020: https://www.who.int/influenza/surveillance_monitoring/updates/2020_09_14_surveillance_update_376.pdf?ua=1
  4. Singapore MOH website: Weekly Infectious Diseases Bulletin (September 2020): https://www.moh.gov.sg/docs/librariesprovider5/diseases-updates/2020_week_38.pdf

Leave a Reply

Your email address will not be published. Required fields are marked *