an almost non-existent flu season in Utah

Maybe this is a sign that I have been looking at the charts for too long, but this bar chart is cracking me up.

On the left is a bar representing the number of positive flu tests in Utah last flu season. That number was 14,678.

Right, the number of positive flu tests this flu season. That number is 47.

It’s almost ridiculous, isn’t it? For example, if you asked 15,000 people “Is the sky blue or is the sky a chocolate chip cookie?” You would always get over 47 people picking cookies. You just don’t see a 99% discount on anything.

And yet, this is what we have here. We have seen a virtual elimination of the influenza season, much smaller than any influenza season on record. Here’s another incredible graph comparing this year’s flu season to previous years in Utah using data from the state Department of Health:

The red line is this year. I had to chat with our graphic designer about how to make sure we differentiate that red line from the x-axis in the print. This is not a problem that we have frequently!

So what is going on? Let’s break it down.

Why do so few people get the flu?

The first thought I had, as an often suspicious person, was that we don’t really test for the flu anymore. After all, people might suspect that flu-like symptoms are due to COVID-19 and proceed from there.

But it turns out that testing isn’t the problem at all. This flu season, we’ve tested 1.15 million people in the United States for the flu so far, up from 1.2 million last year. We do roughly the same number of tests. But understand this, last year 1 in 5 tests came back positive for the flu, while it is now 1 in 625.

The real reason the flu is down is that all the precautions we’ve taken to mitigate the coronavirus have decimated the flu, because the flu is a much less contagious disease than COVID-19.

We have already introduced the key statistic known as R0: this is the average number of people that a sick person will infect. An R0 greater than 1 and disease spreads quickly. An R0 less than 1 and a disease will eventually go away. For seasonal flu, R0 is usually around 1.3. For the 2009 swine flu pandemic, it was 1.46.

For COVID-19, R0 is estimated to be around 3.3 without intervention. Scary.

But of course we are doing all kinds of things to change that: limiting groups, wearing masks, washing your hands more, etc. Right now, with our interventions, our R0 for the coronavirus is hovering at 1 – now, with vaccination, we’re below 1. But those same interventions that reduce the transmission of coronavirus disease by 70% mean that the flu has never had a chance.

By the way, the flu isn’t the only bug that has been nearly eliminated due to COVID-19 precautions. According to Germ Watch of Intermountain Healthcare, they found “minimal activity” of rhinoviruses, adenoviruses and seasonal coronaviruses (those that are not COVID-19), and simply “no activity” of RSV, enteroviruses. and whooping cough in the last week.

Estimate the impact of reducing influenza

You may have noticed that I was referring to the positive influenza lab results, and you know this as well as I do, not everyone who gets the flu gets tested, by far. Fortunately, we have a 2019 study from the Centers for Disease Control and Prevention and the Utah Department of Health that specifically attempted to determine the number of flu cases in Utah during the 2016-2017 and 2017 seasons. -2018, based on the limited number of influenza cases. the data we have.

Essentially, these researchers used the counted number of flu-related hospitalizations and extrapolated from there, breaking them down by age group. To give you an idea, there were 2,169 confirmed hospitalizations in 2017-18, but the state knows hospitals often don’t test patients for the flu, so they estimated 3,900 hospitalizations that season. They also know that most flu patients never go to hospital and estimated that 160,000 people have seen a doctor, nurse or pharmacist for the flu. Of course, some do it on their own and never see a medical expert at all; they multiplied again and estimated that there were 338,000 cases of the flu that year in Utah.

By the time you hit that number of multiplications, there’s a pretty wide confidence interval: they estimated with 95% confidence that the actual number of influenza illnesses was between 285,000 and 391,000. Basically, between 9% and 13% of Utahns contracted the flu that year. It was about 7% to 11% the year before.

If you do those same calculations with the number of hospitalizations this year – remember, a paltry 14 – you end up estimating that about 2,180 Utahns have contracted the flu this year. Wow. We have saved an estimated 330,000 influenza illnesses.

How does the reduction in influenza illness compare to the increase in COVID-19 illness? The number of confirmed COVID-19 cases in Utah is around 385,000. Now we know from previous research that the total number of Utahns who have been ill with the coronavirus is much higher than that.

But remember, COVID-19 is more dangerous than the flu. We typically see between 300 and 400 deaths from influenza and pneumonia each year in Utah, and we have seen 2,122 confirmed deaths since the start of the pandemic due to COVID-19. The state does not release the total number of flu deaths until after the flu season is over, but with just 14 hospitalizations, you can safely estimate flu deaths so that they can be counted with one hand. It might even suck.

What does this mean for the future?

Believe it or not, but some people are concerned that we haven’t had more people with the flu. In particular, this Politico article, titled “The pandemic has dramatically reduced influenza cases. It could backfire on you. exposes the argument.

Basically, because there are many types of flu – regular flu A, flu B, swine flu, etc. – we use each year’s flu data to guess what’s most likely to circulate next year, then create the flu. vaccine that stops what we think is most common. But with limited data, will we be able to do it?

Even in this pessimistic article, however, there were some pretty clear signs that everything will likely be fine. First, the previous low flu seasons (although they are nothing like this year) have not meant higher flu seasons in the past. Second, a member of the Food and Drug Administration’s vaccine advisory committee said that even “low levels of the virus this season still allowed the team to choose strains for the vaccine. He didn’t care.

Second, even when things return to normal, I suspect a number of people will be more cautious of infectious diseases than they were in years past. Coming to work with a cough will not be generally accepted or even encouraged as before. We will see some people – not a majority, but some – wearing masks at airports or in large crowds. It won’t have a huge impact, but when the seasonal flu has a transmission rate of just over 1, even small changes matter a lot.

We will see next winter to what extent precautions are taken, both for the flu and for the coronavirus, which will always be with us. But there is no doubt that the reduction in influenza cases and deaths this season is a beacon of hope for the dark cloud that is COVID-19.

Andy Larsen is a data columnist. He is also one of the Salt Lake Tribune’s Utah Jazz beat writers. You can reach him at [email protected].