Another Covid Mystery

Flu season is here and we have been told to expect a possible "twindemic" by the experts.

A horrible winter that will see us battling both Covid-19 and the seasonal flu.

Dr. Anthony Fauci is among those raising the alarm.

Fauci, the nation’s leading infectious disease expert, has warned the daily number of new coronavirus cases in the U.S. remains dangerously high, especially as the forthcoming flu season threatens to complicate the nation’s response to the pandemic.

“You can’t enter into the cool months of the fall and the cold months of the winter with a high community infection baseline,” Fauci said. He added that the positivity rate, or the percentage of tests that are positive, is “going in the wrong direction” in more than 30 states.

There have been a lot of news reports telling people how important it is to get a flu shot this year. This is an example from CNN.

With a black suit jacket shrugged off her left shoulder, Michigan Gov. Gretchen Whitmer didn't flinch while getting a flu vaccination on live television in September.

"Literally the easiest thing I will do today," said Gov. Whitmer, who called the press conference to underscore preparations for this coming flu season.

"Preventing the flu will help us save lives and preserve the health care resources we need to continue fighting Covid-19," she said. "It's more important than ever."

What is interesting about all of this hype is that as one looks at the facts around the world the evidence seems to suggest that the flu has disappeared at the same time that Covid-19 took hold.

For example, look at this comparison of positive cases of the flu and Covid in 2020 while also looking back at flu cases in 2019.

Notice how flu cases in North America in 2020 were running ahead of cases in 2019 until the week of March 9 (Week 10). The next week flu cases starting dropping quickly. That also included positivity rates. This is exactly when the Covid pandemic started in North America.

Look at the 2020 cases and the positivity rates compared to 2019 for the rest of the year. One month after Covid starting take hold in mid-March, flu cases in 2020 were down 97% from 2019.

It almost as if Covid-19 pushed the flu out of the way.

Hat tip to Kyle Lamb for putting me on to this topic. 

Source: https://twitter.com/kylamb8/status/1317186399909675009/photo/4

It is simply amazing.

This is data from the week ending September 27, 2020 (Week 40) that Phil Kerpen summarized from the CDC weekly influenza surveillance report.

Confirmed fly cases are down 96% from last year in the same week at the beginning of this flu season!

Of course, someone could look at this data and correctly conclude that the 2020 flu season was starting to wind down when Covid-19 hit North America in March so this might not be a fair comparison. This year's flu season is also just beginning.

How about if we look at countries in the Southern Hemisphere which were entering the peak flu seasons of their Fall and Winter when Covid was striking them in the March-September time frame?

These charts are all from the WHO Global Influenza Surveillance and Response System.

Let's look at what the incidence of flu has been in 2020 compared to 2019 in the winter seasons in South Africa, Argentina and Australia. Three different countries on three different continents in the Southern Hemisphere.

South Africa.

Argentina.

Australia.

It is as if the flu has disappeared while Covid is present.

Some people might look at this and say that this drop off has been caused by social distancing and masks.

However, if that is the case why are Covid-19 cases still present and increasing in these countries?

They are both viruses. Why did mitigation efforts stop the flu but not Covid? Why would one be affected this significantly and the other isn't? 

It defies common sense not to mention "science".

You can see that in Sweden's case numbers.

As we know, Sweden never locked down. It kept its schools open. It never applied strong mitigation measures. It has never adopted widespread mask usage.

However, notice that flu cases in Sweden also started to fall like a rock beginning right after the week ending March 14 (week 11) in 2020. After the middle of April there were no more flu cases in Sweden and that remains the case today.

Compare that to the normal trend we saw in 2019.

What was the difference? Covid-19 was circulating in the community.

It will be interested to see what happens in Sweden during this flu season for two reasons.

First, Sweden is not experiencing the significant increase in Covid-19 cases right now that other European counties are. If Covid is not around does that mean the flu will come back?

Second, since Sweden is not doing much in the way of mitigation measures will we see a stronger flu season there than in other European countries?

It will also be interesting to see if we see a twindemic in the United States that Dr. Fauci and other experts are predicting.

This data indicates to me that Covid may be in some way blocking the flu virus from replicating in the population. It is almost as if Covid is bigger and stronger so that the flu cannot get established in the community when Covid is present.

This theory seems to have some support in scientific literature.

Consider this study that was published in The Lancet in September which suggests that one respiratory virus can effectively block another virus in the airway mucosa from establishing itself in the body.

There is other interesting research out there about the interplay of various viruses in the community and in our bodies.

For example, look at this study from 2012 that showed that children who received the flu vaccine were actually 4.4 times more likely thereafter to be be infected with another noninfluenza respiratory virus over the next several months than those who did not get the flu vaccine.

We randomized 115 children to trivalent inactivated influenza vaccine (TIV) or placebo. Over the following 9 months, TIV recipients had an increased risk of virologically-confirmed non-influenza infections (relative risk: 4.40; 95% confidence interval: 1.31-14.8). Being protected against influenza, TIV recipients may lack temporary non-specific immunity that protected against other respiratory viruses.

Early in the pandemic there were some reports that those who had the flu shot were actually at higher risk of catching Covid. Most experts state that is not correct. However, our immune systems are extraordinarily complex. 

As shown in the study above, if the immune response is triggered in one instance does it have the ability to respond as well if attacked in another area? This would seem to be confirmed in the increased mortality we have seen with Covid with other comorbidities. Could it be possible that if flu rates are heading down in the presence of Covid that the benefit/risk equation on getting a flu shot this year has changed compared to other years?

I don't know. However, is it something worth considering when you look at the data above?

In any event, there is good news in all of this.

If the presence of Covid is causing the flu to be less prevalent there may be some additional benefits.

The flu attacks the young at a much higher rate than it attacks older people.

CDC data suggests that children 0-4 are infected by the flu at a rate about 3 times those who are age 65+. School age children 5-17 are twice as likely to catch the flu as their grandparents.

Less flu might mean less deaths in the young. The data currently shows that Covid is less deadly than the flu for those under age 48.

Covid has a higher mortality rate for those over age 48 compared to the flu.

Source: @Covid19Crusher

The flu is actually calculated to be 2.5x more lethal to the young than the old.

Covid is 2.5x more lethal to the old than the young.

Is Covid a cure for the flu?

We will see.

It is just another Covid mystery right now.