What’s happening with covid in the UK?

I couldn’t find the graph I wanted to work out how worried to be about coronavirus hospitalisations, so I made it…

I chose to plot things like this because I think it’s a really neat way to make sense of what’s going on with coronavirus (or perhaps see that we’re annoyingly just short of enough data to really make sense of it right now—but, if we wait for the few weeks for the data to tell us how worried to be, it’ll be too late).

The other thing that’s a bit nerve-wracking is that even though we think the number of cases being hospitalised with covid has dropped from 8% to 4% thanks to the vaccines—a halving, which is an amazing testament to the power of science—that only actually buys the NHS about two weeks. That’s because cases and hospitalisations are growing exponentially at the moment, with roughly a two-week doubling time.

Exponential growth be crazy, but this is the thing that’s both the defining factor of and really hard to grasp about it: exponential processes multiply by a fixed amount every time period. With covid at the moment, this means doubling every two weeks or so. But our perception is linear: oh, half as many hospitalisations! Great news, we effectively have twice the capacity! Which in everyday life would usually perhaps be too much spare capacity, because most ‘numbers of people’ type phenomena we deal with are linear, not exponential.

But with an exponential phenomenon, it buys you a single doubling time. And, another doubling time after that, you’ll have twice as many cases as space, which means people don’t get care because everything’s rammed, and we need to lock down again before that happens.

If you understand this one simple fact about cases of an infectious disease, you are already way ahead of the Government.

Let’s hope the Government are right to gamble on cases and hospitalisations decoupling further… But I’d feel more comfortable if we reigned things in a bit, especially since two doses of vaccine seem to be effective against the new Delta variant that’s driving this wave—it’s only a few short months until most people are double-dosed, so it seems a bit silly to let things go now.

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