How to detect the very many people who do not have symptoms of Covid-19 or who have not yet developed them?
Since last spring, health and political authorities around the world have been working on this puzzle, without any miracle solution emerging.
In recent weeks, the popular strategy is called mass screening.
Recently implemented at the scale of a city, such as Liverpool in England, a region or even a country, such as in Slovakia or Austria, this method consists of testing in large quantities and regularly.
Objective: to quickly isolate as many silent cases as possible.
As a reminder, never have asymptomatic agents had such a powerful impact in the spread of a coronavirus.
In France, the idea of national screening is not at all on the agenda.
Lack of perspective on the attempts carried out abroad, "very complex operational logistics" ... The Scientific Council called for caution in a note sent in mid-November to the authorities in mid-November and published on Monday.
However, an important clarification, the government advisers - in passing very severe on the “relative failure” of the isolation of people who test positive - recommends carrying out “experiments” at the local level.
These "could be carried out BEFORE the release of confinement n ° 2 in some metropolises".
In other words, by mid-January.
Contacted by us, the Ministry of Health confirms "work" on this hypothesis, but refuses to comment on any agenda.
The key to escaping further confinement?
Unsurprisingly, the Scientific Council mentions two geographical avenues: the Auvergne-Rhône-Alpes and Hauts-de-France regions.
While several researchers have been campaigning for several weeks for Lille and Roubaix to act as guinea pigs for the government, the Auvergne-Rhône-Alpes region had already announced that it would test its citizens from December 16 to 23, in order to protect its "elders" during the Christmas holidays.
A thousand sites across the region, buses deployed in rural areas, 10,000 people mobilized… At the initiative of this volunteer-based project, President LR Laurent Wauquiez is targeting two to four million tests.
Catherine Hill, former head of the biostatistics and epidemiology department at the Gustave-Roussy Institute in Villejuif (Val-de-Marne), welcomes the fact that trials are being launched in the region.
This is the key, according to her, to escape a third wave and a new confinement, in addition to barrier gestures and certain movement restrictions.
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“Today, the cases identified are only the tip of the iceberg, deplores the epidemiologist.
It takes nine to ten days before telling someone if they are tainted and contaminating.
It is far too long.
Suddenly, we cannot follow the transmission chains and isolate in time ”.
As a reminder, we are especially contagious the first days of the disease.
"We are unable to do so on a national scale"
If Catherine Hill's observation is rather unanimous within the scientific community, the same cannot be said of her initial proposal: to test the 67 million French people every ten days, at least until the arrival of 'an effective vaccine.
"We are unable to do so at the national level," says epidemiologist Carole Dufouil, research director at Inserm.
More nuanced about the prospect of a trial in a “well-organized city with efficient laboratories”, she doubts the material and organizational capacities across the country.
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Lionel Barrand, the president of the national union of young medical biologists, also considers this project unfeasible.
And that, even on a city scale.
“I believe that some do not realize the technical means that this represents.
Massive testing involves an insane reorganization and a huge cost.
We would have to give up all our other skills, especially in chemotherapy.
Not to mention that we are already one of the countries that test the most, ”he says.
This biologist also doubts the reliability of antigenic tests, which are at the heart of the system abroad, and should also be in Auvergne-Rhône-Alpes.
The latter are faster than PCR, but could miss one in two asymptomatic.
Lionel Barrand finally wonders about the real usefulness of saliva tests.
“OK, we will have simplified the process with the sputum part, it will be more pleasant for the people tested, but that does not solve the problem of the analytics behind.
We don't have enough machines to read the results ”.
To all these logistical arguments, Catherine Hill replies "political will".
“We have the means!
"She proclaims, protesting in passing against the refusal" without documentation "of the High Authority of Health (HAS) to use saliva tests in asymptomatic cases or to use the contested method of" group tests ".
Slovakia, Liverpool ... efficiency that remains to be proven
These different sounds of the bell do not facilitate the work of the authorities.
Especially since abroad, it is for the moment difficult to decide on the effectiveness of this strategy.
The Slovak or English authorities may well congratulate themselves and promise to relaunch the device in December, the results are unclear.
The decline observed is no more significant there than in other regions having "contented themselves" with partial or total reconfinement measures.
Sign, once again, that there is no miracle cure.
A massive test campaign in Zilina, Slovakia, on November 7, 2020. REUTERS / Radovan Stoklasa
These experiences also raised another difficulty, already highlighted in the field of vaccines: the question of the adhesion of the population to these campaigns.
Especially among the most precarious.
In Slovakia, the threat of quarantine was raised to subdue the refractories, which made it possible to obtain a very high participation rate (between 80% and 90%).
“In Liverpool, we are starting to have many difficulties, also warns Carole Dufouil, epidemiologist at Inserm.
People don't come back for testing, and there are significant socio-economic differences among those who do.
"
Sections of the population difficult to convince
In some of Liverpool's poorest communities, only 4% of the population took part in the test, according to a BBC analysis.
"How do you get people to do the right thing if they are struggling to make ends meet and fear losing their income?"
The payment of 500 pounds sterling in case of isolation is often not enough to allay their concerns, ”summarizes with the British media Annemarie Naylor, director of policy and strategy at the charity Future Care Capital.
The Scientific Council also points the finger at the risk of "an effect of exhaustion of the various actors and the population" in the face of "the need to repeat mass screening every 15 days".
These uncertainties did not in any case discourage Boris Johnson.
The British Prime Minister announced that Manchester, Leeds, Newcastle, Birmingham and Bristol will also be offered a "six-week test wave" from Wednesday, December 2, the date of the partial lifting of confinement.
Or a project now targeting 23 million citizens.
There is no doubt that the French authorities will keep a close eye on this extremely costly bet.
To better apply it when the incidence rate has fallen to a very low level?
This is more or less the method adopted by the city of Wuhan, cradle of the epidemic, after the first confinement.
For a result, it seems, radical.
