Coronavirus: what is R0, this indicator that gave the green light to containment exit?

Published by Laurent P. · Published on 12 May 2020 at 12h53
Despite coronavirus, French have been allowed to get out starting today, May 11th, 2020, as long as they uphold the many safety measures. The containment exit has been made possible thanks to R0, an indicator enabling to follow the evolution of the virus. But what is R0 actually? The editorial board tries to give you an answer.

Even though coronavirus is still not, and far from being so, a bad memory, it is time to exit containment. A possibility to go out again that has not been decided in two shakes of a lamb’s tail. At the heart of the decision of gradually lift confinement, a key indicator, R0… But what is R0? A question the editorial boards tries to answer.

So, what is R0? According to the government, “R0 is a measure of the rapidity coronavirus spreads. Under 1, the virus is under control, over 1, the virus is more and more threatening” one can read on In other words, a “rate of the reproduction of the virus” measuring the average number of people a sick can contaminate around them, “within a specific population not immune or vaccine” our peers at BFMTV says.

If this indicator is above 1 (index “1”) the sick contaminates over one person and the epidemic spreads, but if this indicator is below 1, the sick will contaminate on average less than one person until the virus is eliminated. Hence the utility of lockdown… A contagion rate that was yesterday, Sunday May 10th, at 0.6, as Health Minister Oliver Véran explained on BFMTV. According to him, the goal is set to avoid reconfining the population: “When we will gradually lift confinement, R0 will increase. What we want is that is remains below 1” he explained.

For the record, at the time France was put on lockdown, R0 was above 1, since “one person infected transmitted the virus to 3.3 people on average” as Doctor Simon Cauchemez explained to our peers at 20Minutes. A significant drop and a rate we should keep, to make sure we are done with Covid-19 once and for all.

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