What is at stake for French society with the deconfinement?

The study by the Pasteur Institute published online on April 21, 2020 reveals from more than 70,000 cases in France that the average number of people infected by a COVID-19 patient, called the reproduction number, R0, would have been 3.3 on average in the pre-confinement period. The reproduction number, R0, indicates that the proportion of the population that will be contaminated if the virus is allowed to spread without drastic measures to limit vadical contact (1 - (1 / R0)), i.e., 70% of the population.

In the long term, if it is hypothesized that SARS-CoV-2, similar to SARS-CoV-1, induces transient immunity in humans, at least 70% of the population will eventually need to be immunized so that herd immunity can prevent a second wave of contagion. Without drastic control of case isolation and collective acquisition of barrier gestures, an even greater proportion of the population will have been contaminated.

If the mortality rate remains constant at ~0.5%, then at least 3.5 people out of 1,000 will die from COVID-19, or about ~205,000 COVID-19 victims in France before we can achieve herd immunity. Today, France has only 7,500 resuscitation beds and a COVID-19 patient in a severe condition typically has to stay in intensive care for 2 weeks. In the event of a bottleneck in the healthcare system, the number of victims will be greater.

So far, one embolism in the health care system has been prevented thanks to :

• government-imposed containment since March 17 (which lowered the R0 to 0.5)
• the exceptional dedication of health care workers, which enabled the number of beds in the intensive care unit to more than double, and of emergency doctors to transport patients by train and helicopter to less affected areas

Nevertheless, when the containment is lifted and borders are opened, strict precautions (masks, screening, and isolation of cases) will eventually be necessary to prevent a resurgence of the epidemic.

The lower the reproduction number, R0, the slower the spread of the epidemic, the more we can guarantee the care of the sick and protection of the nursing staff, and the more time we save in finding effective therapies.

It is therefore of paramount importance for all of us to reduce R0 as much as possible:

• reduce the proportion of infected people to achieve herd immunity,
• avoid a new spike in contamination that is too overwhelming for our already strained health care system, and
• buy time before the arrival of COVID-19 treatments or a vaccine.

There are of course many uncertainties about the parameters that control the reproduction number, R0. Nevertheless, since the virus is transmitted via droplets of saliva or via hand contact on surfaces contaminated by the virus,

• wearing masks can significantly reduce the number of droplets expelled, and
• Regular hand washing reduces the likelihood of being contaminated by viruses 'deposited' on contaminated surfaces.

Barriers therefore help to slow the spread of the virus which will ultimately save lives and allow our country's economy to get back on its feet more quickly.