There Is No ‘Casedemic’

Why the rise in COVID-19 cases is very worrying

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Pictured: We’re all in this together, and other reassuring slogans. Source: Pexels

As cases of COVID-19 skyrocket across Europe and the United States, a new myth has emerged to add to our ever-increasing list of coronavirus-related nonsense. The idea is that the current massive epidemic in Europe and elsewhere is not an issue, because this is a ‘casedemic’ — an increase in cases without any concomitant increase in sickness or deaths.

Basically, it’s another way of saying that the pandemic is over, from people who’ve been saying that it was over every month since March.

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Pictured: Not over yet, unfortunately. Source: Pexels

Thing is, this new piece of disinformation is simply factually inaccurate, and is driven by a simple misunderstanding: that the second wave of COVID-19 was dramatically different to the first. In fact, the two waves are much more alike than you’d imagine, because the disease probably hasn’t changed enormously in the last 6 months or so no matter how much we wish that it has.

In other words, while the number of cases that are appearing positive now seems far higher than at the start of the year, in fact what we know is that we missed a huge proportion of cases back in March and actually it’s more than likely that the current wave looks very similar to the first.

This may seem obvious, but let me explain.

My epidemiology mentor, a professor of many years, has a great saying: “remember the denominator”. The denominator of your proportion is the most important part of the equation. Without knowing how the denominator has or will change, we don’t really know anything about the numbers themselves.

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Maths is fun! Source: Pexels

So, what is the denominator here? Well, what we know about coronavirus numbers is usually based on confirmed cases — these are people who have had a test (almost always RT-PCR tests) that has come back positive for COVID-19 and been confirmed by their country of residence as having the disease.

Which gives us graphs like this. So many more cases in the second wave!

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Make your own scary map at Our World In Data

But the thing is you have to remember the denominator. How many tests were we doing in the first wave as compared to the second?

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Pictured: A changing denominator!

This makes our comparisons flawed, at best. Indeed, as we can see from serological studies — where we test lots of people in the population for antibodies to see if they’ve had COVID-19 already — we find that we missed a HUGE number of cases in the first wave. For example, the REACT-2 study of England, which is one of the most robust serological surveys in the world, estimated that 6% of the country had already had COVID-19 by July, equating to about 3.5 million people. In comparison, official figures put the number closer to 350,000 infections, meaning that the country may have underestimated the true figure by up to 10x!

Another way of looking at this is to back-calculate the number of cases from the number of deaths. While case ascertainment changes over time — we test more or less people, and different people are eligible for tests — deaths are a pretty hard endpoint that rarely changes. And since we now have good evidence about the death rate by age for COVID-19, we can use the deaths by age to get a rough approximation of the number of cases behind each death. This is pretty simple back-calculation — the infection fatality rate (IFR) of the disease calculation is:

IFR = deaths/true cases

So to work out the true case numbers, we just flip the equation:

true cases = deaths/IFR

Let’s look at an example. Here’s the graphs of cases and deaths for the United States — looks like a ‘casedemic’ at first glance! Cases rising but a much smaller increase in deaths.

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But, if we perform the back-calculation from the number of deaths by age group…

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Source: Me

Suddenly, the difference disappears! Indeed, it looks like the first wave might have even been a bit BIGGER than the second. This makes perfect sense when you consider that, at least in the United States, the number of tests being done each week in March was in the hundreds of thousands, and limited mostly to people who were being hospitalized for COVID-19. So we missed almost everyone with a mild infection, and cannot have picked up the millions of cases that almost certainly existed at the time.

This trend is repeated across country after country when you look at the serology figures. We simply weren’t picking up as many true cases in the first wave as we are now.

The central thesis of the ‘casedemic’ myth is very obviously false. We know that we must have had many more cases earlier in the year than were recorded — this is not at all a contentious point — and indeed it looks like we are heading for a second March in many places in the world right now.

The depressing thing about COVID-19 is that we can really predict quite well what is going to happen now. When cases rise, it takes a few weeks and then hospitalizations rise. Once hospitalizations rise, it’s only a matter of time until deaths do as well. We can now see this trend playing out across Europe, with France, Belgium, the UK, and numerous other places being swamped by a huge number of severe cases. And while our treatments have improved over the past year, the death rate of the disease is still extremely high across age groups.

When more people get sick, quite a few of them will die.

This is why countries like Sweden, even though they have not yet seen huge increases in deaths, are implementing new restrictions to try and curb the growth in cases. While we can’t really predict the number of deaths in a place without knowing the age breakdown of cases, it’s likely that the massive rise in cases will be followed by a large rise in hospitalizations and deaths.

Because it’s happened before. Yes, deaths lag behind cases, because it takes a median of three weeks from being infected for people to die, and then several weeks after that for deaths to be reported, but this doesn’t mean that the disease has gotten less fatal.

Sadly, the idea of a casedemic is a myth. There is no casedemic.

Just a regular pandemic.

As scary as that is, it’s simply fact.

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