The Batman Cometh (covid)

 In my previous covid post The Third Wave, I made the somewhat cavalier statement that instead of having a 1% chance of dying next year, with covid you had a 1.1% chance.

Now the third wave has fully developed into if anything a bit bigger than the first. Is that assessment worth revisiting?

I think it is, not so much because it was wrong (we'll see) but because it was too general. In particular, mortality from covid depends drastically upon age. Here are deaths by age group from the CDC:

The third wave has developed into an eerily appropriate Batman's second ear. There several things to note about this chart. The red line is 2020, the gray are previous years. But they are not death rates; they are death counts. Death rates climb much more steeply by age. Furthermore, the divisions are not comparable: look at the middle two. 45-64 is a 20-year cohort; 65-74 is only 10. So the apparent indicated rate in the latter should be twice the former.

Even so, it is clear (and quite true) that the effect of covid is bigger with advancing age. It rises from essentially nothing under 45 to about a 30% extra chance of dying (during any given period) at 90.

We can make this more apparent by taking actual actuarial figures and plotting the effect of the extra risk. 

The blue curve is the fraction of the population who (barely) reach a given age. The area under the curve is life expectancy at birth.

The orange is the same curve with covid, calculated with the excess death rates of late December.

That's important, so I'll repeat it. The orange curve assumes that the covid death rates continue all next year at the level of the peak of the third wave.

So what about that 1.1% instead of 1% chance of dying next year? As of now, roughly 0.1% of the US population has already died of covid. If it runs unchecked through the rest of the population, based on Diamond Princess numbers, it will claim another 0.2%. (That would amount to about 1.2 million deaths; we are already at 400,000.)

But critically, the risk isn't linear. If you're under 40, your risk of dying next year is less than 0.2% and covid does not appreciably increase it at all. If you are 70, your normal chance of dying next year would be 2.5%, and covid increases that to 2.9%. That is significant.

The bottom line here is that there simply isn't any one-size-fits-all response to the situation.