An exit strategy for COVID-19

Scotland’s Nicola Sturgeon was first out of the blocks on Thursday with some proposals for lifting the Scottish lockdown. Her government’s “Framework for Decision Making” came a day after Professor Chris Whitty, England’s Chief Medical Offices, made it plain that we are all going to have to live with disruptive social measures for at least the rest of the year, and perhaps until a vaccine can be mass produced. It’s also clear that there needs to be a huge amount of testing, tracing of contacts, and isolation of symptomatic individuals. So how might all this work? One strategy, from mathematicians in France, is to divide countries up into lots of small "cells". These are colour-coded "red" when the virus is actively spreading in that area - and people there stay in lockdown; or "green" when the virus is under control, and people there can go about their business largely as usual. Green areas are allowed to interact freely with other green areas, but not with red areas. This, the creators say, could get us back to normal in about 5 or 6 months. Miquel Oliu Barton from the Paris-Dauphine University told Chris Smith more...

Miquel - We're interested in how to safely and efficiently transition back to a new normal. The idea would be to partition the country into separate components such as counties, towns or suburbs. And then each area would then be labeled red or green. Red, meaning that the virus is not under control and the strict lockdown measures need to remain in place. While green means that the growth rate of infections is low and the future risks appear manageable. So first thing is you need to map the country into little cells, and each of which has a label, red or green.

Chris - And how big are those cells? When you say little cells, what are we talking?

Miquel - About a couple of thousand per country. But we need to bear in mind that all these things are very flexible. For instance, the European Union is already partitioned into countries, and each country is already partitioning to regions and each region is already partitioned into smaller and smaller regions. So the definition of these cells, which should have between 5,000 to 100,000 inhabitants depending on the density, should be left to politicians and epidemiologists and doctors to know what is possible to really enforce, and what makes sense in economic terms.

Chris - And the idea is that if I'm in say, region one, and you're in region two, we would not meet. There's no way that I can have contact with you and give you my virus. So I'm in a green area, you're in red, you can't transmit to me.

Miquel - Yeah. So the idea is some intermediate situation as we are facing today, instead of everyone is locked down in his place. If we identify areas where the virus is under control, we could allow people in the same area, let's say area A which is green, to interact in a more normal way while people in a zone, which is red, B, will stay in lockdown.

Chris - And how long, because this is a critical question, how long would say your red area stay red? So you've got some cases in your area this week. I'm in a green area next door. How long do you stay red?

Miquel - So this is a good question. So far we, based on what we observed very informally from the media, we are assuming that a zone is remaining red for between 14 to 35 days, which can depend on the country or the area's hospitals.

Chris - Right. And you'd reinforce this. So you keep testing the red areas and the green areas for surveillance purposes. As long as you keep not detecting virus circulation. After that time had elapsed, a red area becomes a green area.

Miquel - Yes. So after one cell, which is a small zone, has been proved to be handling the virus, then you could give it a label green.

Chris - Can we talk about the practicalities of this just for a minute? How feasible is this? Because of course we've got very used to the fact that some parts of the country are nice to live in and other bits are nice to work in. So we commute between the two. There are many people who will end up then entrapped still in a green area, where they live, but work is in a red area and they won't be to go to work.

Miquel - Yes. So that's a very good question, and that's why it is very important in defining these zones, these predefined zones, before we go into the labels, to take into account these commuting zones. We would like, first of all, to open commuting zones. So make sure that one big area, let's say the metropolitan area surrounding London, if the whole area was green, that would be a very good news. And we could open the economic and social interactions within this zone. Even though the whole UK is not having a control of the virus. We need to define these areas in a way that is both enforceable and meaningful in terms of economic and social interactions.

Chris - And if you run your model, how long does it predict it will take for a country on the scale of the population of the UK or France, in order to end up with the entire country being green, wall-to-wall green, back to business as usual.

Miquel - Yeah. We ran a simulation on a very simplified mathematical model. We imagine that the country is divided into cells like a chessboard. What is interesting is that we get something between two to five months for a country like the UK or France, and actually it depends on a very critical parameter, which is; what's the probability that at any point in time a green zone becomes red again, if it's slow enough, then we're driven by these exponential growth to a big green zone. If this parameter is big, then of course we go from red to green and to green to red forever.