Let’s begin by imagining two simple scenarios for coronavirus.
A: each case infects 2 others in a week.
B: each case infects 3 others in five days.
I’m making these up, but bear with me. Assuming each case infects this many and no more, and is infectious only for this long, after 10 weeks, scenario A has clocked up about 2,000 cases. B is heading rapidly to 10 million.
Such is the power of repeated multiplication that A also approaches 10 million about three months later. But it would, at least, give us valuable time—and could imply a lower peak.
An inch and a mile
What’s striking is how differences that might seem marginal at the outset can entail wild divergence. It’s reminiscent of Chaos, and a warning to those who think they know how this will play out: uncertainty needs only an inch to take a mile.
Is either scenario likely? I’ve no idea. No “real” model would be as neat as my formula—that much we can say, as there’s plenty more than an inch of uncertainty about how any scenario will unfold. And that’s the point: every uncertainty could make any of us hopelessly wrong.
Our fallibility isn’t much helped by trying to take control of events. Sure, we can change our behaviour with things like hand-washing and self-isolation measures, and try to disrupt the virus. To some extent, we’ll succeed. Experts who can tell us how to go about it will be invaluable—I’m not for a moment claiming they know nothing at all.
But how the public will react, and with what effect, is hard to say. For instance, we might not do as we’re told. Shut down our sporting events and we might go elsewhere. We’re both unclear what the virus will do and unclear what people will do.
If you’re not feeling uncertain yet, you should be—because it gets worse. Estimates of how many will die range from less than 1 per cent of those infected to over 3 per cent—a difference of well over half a million people if half the UK population falls ill.
The challenge for public health
The uncertainties, in short, are huge. Playing with them can seem grotesque…