The COVID-19 pandemic has put the world to the test.
Never before have we been so aware of the many ways we come into contact with innumerable others.
How we come out of lockdown is the next challenge.
It is important to avoid a resurgence of the virus while minimizing the societal and economic damage.
Proposals range from creatingherd immunityto keeping the lockdown intact until the development of a treatment orvaccination.
We are part of a group of mathematicians and economists specializing in modeling random and uncertain situations.
This is in line with other ideas such as keeping limitations only for high-risk groups.
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Ourrecently published proposalis based on two key elements.
And second, progressively joining these green zones together once it is safe to do so.
But such partitions are far from complete.
In France, where we are based, people are asked to staywithin 1km of their homes.
This would, of course, represent a step up in state-enforced control in many countries.
Such zoning measures have been successfully implemented in several areas in China, notablyWuhan.
This would reduce links between different areas and prevent the virus from traveling throughout the territory.
Disconnecting a human online grid.
Each cell is labeled red or green depending on its current status regarding COVID-19.
In red cells, the situation would be similar to lockdown.
The sanitary measures, restrictions on openings of shops and restrictions on leaving your house would remain in place.
In contrast, life would progressively go back to normal within green cells.
Returning to our Parisian example, all arrondissements could successively be joined together to eventually reunite the city.
After a number of days, all cells return to green (step 1).
After seven days, the green cells merge to form larger green zones (step 2).
After seven more days, the green zones merge into a larger green zone (step 3).
Testing and zoning would of course not be perfect.
Some green zones would therefore inevitably show a resurgence of infections, and so cease to be green.
A new infection is detected in a green zone (step 1).
Green-zones are revised to contain the virus (step 3).
A country such as the UK, our simulations suggest, could be reunified within two to four months.
This assumes sufficient sanitary measures are maintained, and testing becomes more widely available.
While green zone merging requires a careful process, it is efficient.
To reap the full advantages that the practice of green zoning offers, important policy choices must be made.
The definition of zones needs careful consideration of social and economic ties.
The rules applying for each zone would need to be clearly defined.
The time has come to consider an exit strategy.
Our mathematical modeling suggests that some version of green zoning would offer this.
