Why they’re so strict about preventing the spread of Coronavirus…

it’s exponential, not arithmetical

This family of pixies is self-isolating, but the human is clearly getting way too close

We all know there are very good reasons why authorities all round the world are imposing restrictions on so that we keep away from other people in order to reduce and hopefully stop the spread of the Covid-19 virus. It’s extraordinarily virulent, so that means keeping away from other people — not touching other people, not touching things other people have touched, and not being in the same air space as other people. And that applies to us whether we have symptoms currently, have recovered from the virus, or are feeling perfectly fine — we can still pass it on in any of these circumstances. Covid-19 is extraordinarily transmissible, and it hangs around on things for an unusually long time. Even air kissing at two metres distance is dodgy, we’re now learning.

What most of us probably haven’t realised is just how it is that the infection can spread so quickly to so many people. And the explanation for that is that the spread is exponential rather than simply arithmetical. In other words, two contacts do not mean twice the potential for spreading the virus load as one — it’s much higher than that.

Here’s how it works. Let’s say you’re in any of the sorts of contact mentioned above with ten other people over say a week. That potential virus transfer equals 10.

If each of those people is then be in touch with ten other people during that same week, that part of the transfer equals 10x10 = 100

If each of those people is also in touch with another ten other people, that transfer equals 100x10 = 1,000

If each of those people is then be in touch with ten more people, that transfer equals 1000x10 = 10,000

So the steps — which can happen during that same week — go from 10 to potentially 10,000 in just four stages. And further stages will also be happening simultaneously, taking the knock-on effects even higher.

Now, let’s say that instead of ten people, you’re in touch with twenty people in that week — double the number — and that each of those people contacts twenty other people too. Just for that first stage, that transfer equals 20x20 = 400. Then the next simultaneous transfer equals 400x20 = 8,000, then 8,000x20 = 160,000, then 160,000x20 = 3,200,000. So in doubling the numbers of contacts people are making, these four stages take the numbers from 20 to potentially 3,200,000 in a week. Of course, not all these contact will catch the infection, but you can see how the chances are hugely enhanced by making more contacts.

So that’s why they’re going on about it so much. That’s why they’re telling us not to get close to each other, and not to touch stuff other people have touched. It’s not just people who have got the infection that are passing it on — people without symptoms and even without the virus can pass it on by touching things that people with it have touched.

But if you managed to limit your contact in the week to just two other people, then the figures would be like this. For the first stage, that transfer equals 1x2 = 3. The next simultaneous transfer equals 3x2 = 6, then 6x2 = 12, then 12x2 = 24 for all four stages. That’s noticeably better, I think you’ll agree, than 10,000 or 3,200,000. And possibly manageable.

The best option of all, of course, would be to not be in contact with any other new people ie that you’re not living with. Then your first stage contacts will be 0, your second stage contacts will be 0, your third stage contacts will be 0, and your fourth stage contacts — and all other stages — will be 0. That makes a total of: ….yes, zero. Simple — but not easy.

I hope this doesn’t depress you, but rather makes you feel that all the efforts you are making to minimise your physical contacts and self-isolate where necessary are very much worthwhile, and if we all do it, this will hugely shorten the time taken to get through this.

One final optimistic note: people are talking about social distancing, but it’s not really social — it’s physical distancing. We can be more socially connected than ever these days. For more on this, see my follow-up blog, linked below.

Follow-up blog: “Corona: It’s not all bad news”