The R0 is used to measure the extent of the epidemic and must remain at its lowest in order to avoid a new epidemic wave when the containment is lifted.
What is R0? Known as “R zero”, this is the reproduction rate of infectious diseases, that is to say the number of people that a contagious individual can infect. Used on a population that has not been vaccinated or immunized against an infectious agent, the R0 is calculated using three factors: the probability of transmission, the contact rate and the duration of contagiousness.
“If the R0 is greater than 1, a patient will infect more than one person, so the epidemic will grow. If it is less than 1, little by little the sick infect fewer people and therefore the epidemic can subside or even disappear.Olivier Véran recently explained.
The benefits of containment on the R0
The measures put in place by the government, starting with containment, aim to reduce these three factors. At the start of the lockdown, thee R0 of Covid-19 fluctuated between 3.4 and 3.5 in France, appearing as a highly infectious agent.
“The influence of containment has been very important, it has reduced the rate of transmission of the virus by 84%explained Doctor Simon Cauchemez, head of the mathematical modeling unit for infectious diseases at the Institut Pasteur, quoted by 20 minutes. Before confinement, an infected person transmitted the virus to an average of 3.3 people. Thanks to the confinement, the R0 rose to 0.5, with around 700 intensive care admissions per day before, to around 200 in mid-April. As of May 11, 10 to 50 intensive care admissions are expected each day.”
The risks of an R0 greater than 1
Today, after almost 8 weeks of confinement, “the R0 of the coronavirus in France is 0.6”, confirms to our colleagues Dr Benjamin Davido, infectious disease specialist at the Raymond-Poincaré hospital in Garches, in the Hauts-de-Seine. However, should we fear a further rise in R0 from May 11, the date of the lifting of containment? An R0 equal to or greater than 1 would mean that the virus is circulating actively again and that a second epidemic wave is to be feared. Such a scenario would lead to a new saturation of our health system and a possible second confinement.
The scientific council insists on the importance of keeping the R0 below 1: “There are major disparities between very large cities like Lyon and regions like the Center of France which are not affected by the epidemic, explains Professor Jean-François Delfraissy, president of the Covid-19 scientific committee. We are going to come out of confinement with the R0 which will be at different levels and therefore with a different number of cases. Which made us talk about having deconfinement by region, but it was extremely difficult given the population movements that will exist..”
The challenge of this recovery will therefore be to restart social and economic life, while containing the spread of the virus, with which we will have to learn to live in the coming months.
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