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Home » COVID-19 pandemic effect on 2020-21 flu season – good and bad news

COVID-19 pandemic effect on 2020-21 flu season – good and bad news

Last updated on September 28th, 2021 at 12:48 pm

The COVID-19 pandemic has been nothing but bad news, but the near disappearance of the 2020-21 flu season has given us one tiny bit of good news among a metric tonne of public health bad news.

Despite the weird and unfounded myths from the COVID-19 deniers, the only reason why this flu season is so mild is because of the public health strategies to contain the COVID-19 pandemic.

That’s it – it’s nothing more dramatic than that. 

Comparing flu seasons

These two images of the flu season as of week 3 in 2020-21 vs 2019-2020 flu seasons show dramatically how different things are.

For the week ending January 18, 2020 (just a couple of months before the start of the COVID-19 pandemic) most of the USA had either “High” or “Very High” levels of influenza-like illness (ILI). For the week ending January 25, 2021, all states have minimal levels of ILI except for Oklahoma, which has a moderate level. I could find no explanation for the higher level in Oklahoma other than it is a more conservative state and hasn’t exactly been at the forefront of public health initiatives. 

For the week ending March 20, 2021, the whole of the United States was at green status with minimal levels of flu.

This is a graph of the percentage of patients who present with ILI to healthcare centers:

COVID-19 pandemic flu season

As you can see, the 2020-21 flu season is showing nearly the lowest percentage of visits for the past 8 years except for potentially 2011-12. In fact, the percentage of ILI visits is almost at the level that is predicted for the “off-season” for influenza, such as the summer.

Amazingly, there has been just one reported pediatric death from the flu during the 2020-21 flu season, compared to the usual approximately 200 annual pediatric flu deaths.

flu seasons COVID-19 pandemic

Now, as I have written frequently, correlation is not necessarily equivalent to causation. There could be a lot of reasons for these influenza incidence observations that have nothing to do with COVID-19 directly, so we should interpret it with caution. For example, a couple of reasons could be:

  • the COVID-19 pandemic has influenced to varying extents health-seeking behaviors – many people are not going to the hospital fearing that it puts them at risk of COVID-19
  • the staffing of hospitals may have diverted resources from identifying and treating ILI.

However, the World Health Organization (WHO) recently published a report that showed that other areas of the world had much lower levels of influenza:

  • In the Southern Hemisphere, countries observed influenza levels during their winter that was approximately equivalent to inter-seasonal (their summer) levels.
  • In the Northern Hemisphere, influenza activity has been below inter-seasonal levels observed during the past few years.
  • Other specific areas, such as tropical South America, tropical Africa, southern Asia, and Southeast Asia reported low or even no flu activity.

Additionally, the CDC states that:

Based on NCHS mortality surveillance data available on January 28, 2021, 14.8% of the deaths that occurred during the week ending January 23, 2021 (week 3), were due to pneumonia, influenza, and COVID-19 (PIC). This percentage is above the epidemic threshold of 7.1% for week 3. Among the 3,043 PIC deaths reported for this week (week 3), 2,102 had COVID-19 listed as an underlying or contributing cause of death on the death certificate and seven listed influenza, indicating that the current increase in PIC mortality is due primarily to COVID-19 and not influenza.

The drop in influenza activity seems to be closely related to many of the recommendations by public health authorities across the world – wash your hands, wear a face mask, and maintain physical distance from strangers. 

Because COVID-19 and influenza transmission routes are fairly similar, it is plausible that all of the public health efforts with the COVID-19 pandemic have vastly reduced flu activity. In fact, CDC researchers, in a peer-reviewed article, concluded:

Following widespread adoption of community mitigation measures to reduce transmission of SARS-CoV-2, the virus that causes COVID-19, the percentage of U.S. respiratory specimens submitted for influenza testing that tested positive decreased from >20% to 2.3% and has remained at historically low interseasonal levels (0.2% versus 1–2%). Data from Southern Hemisphere countries also indicate little influenza activity.

What are the implications for public health practice?

Interventions aimed against SARS-CoV-2 transmission, plus influenza vaccination, could substantially reduce influenza incidence and impact in the 2020–21 Northern Hemisphere season. Some mitigation measures might have a role in reducing transmission in future influenza seasons.

COVID-19 pandemic and flu season conspiracies

I think that it’s pretty clear that there is a strong correlation between our public health activities with COVID-19 and the reduction in influenza activity across the world during this flu season. But that doesn’t stop the vaccine and COVID-19 deniers from dismissing this with their weird conspiracy theories.

The biggest conspiracy theory about the 2020-21 flu season is that somehow doctors are faking COVID-19 pandemic numbers by moving all of the flu cases into the COVID-19 category.

This graph shows how ridiculous the conspiracy theory is that flu cases are being intentionally or unintentionally counted as COVID-19:

See those yellow areas? If the COVID-19 pandemic was a big hoax then we would expect to see cases no different than a typical flu season. Well, this pandemic is no flu season, it’s orders of magnitude larger.

Moreover, when a patient presents to the hospital with COVID-19 symptoms, they are generally tested for flu and SARS-CoV-2, because a flu patient is treated much differently than a COVID-19 patient. If anything, hospitals across the world are testing for flu more frequently than ever.

Of course, there’s another problem with this conspiracy. There are literally a million, maybe more, healthcare workers across the world triaging patients to determine if they have influenza or COVID-19. If the CDC/WHO/FDA/Joe Biden/Justin Trudeau/my daughter’s pet snake were running this conspiracy, why on earth aren’t their thousands of doctors, nurses, labs, orderlies, administrators, and my daughter’s pet snake not posting to social media about how they are hiding the numbers.

They aren’t posting because they aren’t hiding any numbers.

One bit of flu season bad news

All of the numbers for the 2020-21 flu season are outstanding. Despite the horrific toll of the COVID-19 pandemic, at least we didn’t have to contend with a massive flu pandemic that usually kills hundreds of thousands of people worldwide every year.

Unfortunately, this does have one important consequence. Data from the northern hemisphere is used to determine the antigens in the flu vaccine for the southern hemisphere (remember the flu seasons for each hemisphere are offset by about this six months). And the data from the previous southern hemisphere flu season is used to determine the flu vaccine antigens for the 2021-22 flu season.

The problem then becomes that the teams that review the possible antigens and give recommendations have limited data on circulating strains of influenza. And that may mean that we aren’t protected against a powerful flu strain during the upcoming year.

Yes, that is a substantial worry for the scientists and public health specialists who are responsible for protecting us against a huge flu outbreak or epidemic.

Photo by Kristine Wook on Unsplash


I think there is plenty of solid evidence from scientific research that establishes that dealing with the COVID-19 pandemic has crushed the normal influenza activity across the world. In fact, it makes me think that I might wear a mask every winter even if we end this pandemic and even if I get the flu vaccine.

Anecdotally, and we know that’s not data, I’ve spoken to physicians across the world that the numbers of respiratory disease (non-COVID-19 of course) and gastrointestinal illnesses that they see have dropped precipitously. Sure, that may also be a result that people aren’t willing to go to a hospital or physician’s office because they are more afraid of COVID-19. But it also could mean that wearing masks and washing our hands thoroughly have stopped other diseases.

That being said, we should all get the flu vaccine just in case the flu decides to start up late. And the flu vaccine is safe and effective unless you have some deranged beliefs about it.

This fall I will be wearing a mask, washing my hands thoroughly, and getting the flu vaccine because I think it should be our culture now. You will be protecting yourself, and as a benefit, you will be protecting the people around you.


Michael Simpson

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