May 10 JDN2458978

You’d think after being in this pandemic for several weeks we would now have a clear idea of the fatality rate of the virus. Unfortunately, this is not the case.

The problem is that what we can track really doesn’t tell us what we need to know.

What we can track is how many people have tested positive versus how many people have died. As of this writing, 247,000 people have died and 3,504,000 have tested positive. If this were the true fatality rate, it would be horrifying: A death rate of 7% is clearly in excess of even the 1918 influenza pandemic.

Fortunately, this is almost certainly an overestimate. But it’s actually possible for it to be an underestimate, and here’s why: A lot of those people who currently have the virus could still die.

We really shouldn’t be dividing (total deaths)/(total confirmed infections). We should be dividing (total deaths)/(total deaths + total recoveries). If people haven’t recovered yet, it’s too soon to say whether they will live.

On that basis, this begins to look more like an ancient plague: The number of recoveries is only about four times the number of deaths, which would be a staggering fatality rate of 20%.

But as I said, it’s far more likely that this is an overestimate, because we don’t actually know how many people have been infected. We only know how many people have been infected and gotten tested. A large proportion have never been tested; many of these were simply asymptomatic.
We know this because of the few cases we have of rigorous testing of a whole population, such as the passengers on this cruise liner bound for Antarctica. On that cruise liner, 6 were hospitalized, but 128 tested positive for the virus. This means that the number of asymptomatic infections was twenty times that of the number of symptomatic infections.

There have been several studies attempting to determine what proportion of infections are asymptomatic, because this knowledge is so vital. Unfortunately the results are wildly inconsistent. They seem to range from 5% asymptomatic and 95% symptomatic to 95% asymptomatic and 5% symptomatic. The figure I find most plausible is about 80%: This means that the number of asymptomatic infected is about four times that of the number of symptomatic infected.

This means that the true calculation we should be doing actually looks like this: (total deaths)/(total deaths + total recoveries + total asymptomatic).

The number of deaths seems to be about one fourth the number of recoveries. But when you add the fact that four times as many who get infected are asymptomatic, things don’t look quite so bad. This yields an overall fatality rate of about 4%. This is still very high, and absolutely comparable to the 1918 influenza pandemic.

But the truth is, we just don’t know. South Korea’s fatality rate was only 0.7%, which would be a really bad flu season but nothing catastrophic. (A typical flu has a fatality rate of about 0.1%.) On the (deaths)/(deaths + recoveries) basis, it looks almost as bad as the Black Death.

With so much uncertainty, there’s really only one option: Prepare for the worst-case scenario. Assume that the real death rate is massive, and implement lockdown measures until you can confirm that it isn’t.