Should we screen all French people at once to control the epidemic?

Illustration of a PCR test in Nice.

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• Emmanuel Macron himself has recognized that the “test, alert, protect” system put in place to stem the Covid-19 epidemic is no longer effective.

• For epidemiologist Catherine Hill, the solution would be to test the entire population during this confinement.

• But?

  according to biologists, this recommendation is impossible to implement.

That's it, France is once again cloistered.

Since midnight Thursday evening, France has entered into confinement, for a minimum period of four weeks.

An ultimate solution taken by the government to face an epidemic that has grown out of control.

The “test, alert, protect” system put in place to stop the spread of Covid-19 is no longer effective, Emmanuel Macron acknowledged on Wednesday during his televised address.

"The bet to bet everything on the strategy of testing, alerting, protecting" is effective "with a few thousand cases per day, today we have between 40,000 and 50,000 contaminations", lamented the Head of State.

So how do you go about testing more effectively?

What if the solution was to screen everyone all at once?

This is what Catherine Hill, epidemiologist and biostatistician advocates.

Would it be useful to better control the epidemic?

Would it only be logistically feasible?

The flaws in the French screening strategy

If France initially lacked logistical, human and material resources to launch massive screening, its strategy quickly relied on screening symptomatic people, their contact cases and people exposed to the virus in the course of their duties.

“A strategy that is not in phase with the reality of the circulation of the virus, deplores Catherine Hill.

This only identifies a small fraction of the contaminations.

Between May 13 and June 28, the identified cases corresponded to only 10% of real cases, according to a study conducted by Vittoria Colizza, research director at Inserm and specialist in the modeling of infectious diseases.

At the same time, it was estimated that 4.5% of the population had contracted the coronavirus, which corresponds to at least 3 million people.

This is much more than the cases officially recorded during this period.

The authorities have also relied heavily on the identification of clusters, but between May 9 and October 12, the sources of contamination only represented 8% of the cases identified.

This screening approach says nothing about the transmission of the virus, ”said the epidemiologist.

During his speech, Emmanuel Macron said that in recent days, for 50,000 daily contaminations identified, there were probably as many that were not detected, and that around 100,000 contact cases were called as part of contact tracing.

Figures that no longer allow this strategy to be maintained.

“Especially since we estimate that the identified cases correspond to only a quarter of the real cases, underlines Catherine Hill.

Today, we wait on average three days after the onset of symptoms to test a person, while symptoms appear five days after infection.

Then the results are given on average two days after the sample: ten days after the contamination.

We realize that the sick are contagious when they are no longer.

It is too late to prevent them from contaminating around them, the contaminations have already taken place.

And at that point, we look for their contacts who have themselves already infected around them.

This is why we have never controlled the virus ”.

The forgotten asymptomatics

The deadlines "vary greatly from one zone to another, tempers Dr. François Blanchecotte, president of the Union of biologists.

In my laboratory (in Indre-et-Loire), we are able to deliver test results within twelve hours.

The problem is, we are at 23% positive cases.

And of course, the more we test, the more we find, but if people don't stay at home, that's no use.

This is why only confinement can break the chains of contamination ”.

And to immobilize asymptomatic people - who are contaminated and contaminating without knowing it - who have never really been specifically integrated into the screening strategy.

“We're not looking for them, so we can't find them,” says Catherine Hill.

All this explains the discrepancy between the identified cases and the real cases: the screening strategy in France was obsolete even before being launched: the first publications indicating that the virus circulated very quickly and that half of the contaminating people were asymptomatic date back to early April, so we have known for a long time ”.

"You have to confine to test everyone"

Hence this return to the confinement box.

But for Catherine Hill, "it is not enough to confine to confine, it is necessary to confine in order to test everyone, allocate the necessary means for a mass screening campaign and manage to test the entire population in two weeks".

The objective: "to find all the positive and contagious people at once to isolate them immediately and thus break all the chains of transmission," she recommends.

Without this, the virus circulates, especially as this light confinement is less strict than the first, and therefore less effective.

The virus will continue to circulate with essential workers, in stores, in transport, in hospitals, in nursing homes, wherever people go ”.

But is a screening of this magnitude feasible in such a short time?

"We are not at all comparable to China, which was able to test ten million people in a few days in Wuhan," says Dr Blanchecotte.

We have neither the means nor the logistics ”.

In practice, “to screen the entire population in two weeks, 35 million tests would have to be done per week, which is 17 times more than what is currently being done.

However, we are at the maximum of our capacities, adds Stéphanie Haïm-Boukobza, head of the infectious disease center of a laboratory and member of the Union of Young Medical Biologists (SJBM).

Considerable efforts have been made to increase screening capacity, she insists.

At the start of July, we were performing 300,000 tests per week, and today we are at almost two million.

But there are limits that are difficult to overcome: in my laboratory, we already work 24 hours a day, 7 days a week ”.

"There are not 65 million tests available today in France"

For Catherine Hill, “between the PCR tests, the saliva samples and the antigenic tests which make it possible to obtain a result in thirty minutes, testing the entire population should be feasible.

One could also use PCR self-tests, as in the United Kingdom, where authorities have tested 680,000 people who have self-sampled from their nose and throat, she suggests.

And the technique of pooling, which consists of performing grouped PCR tests, is also a way to save time and reduce costs.

Finally, the search for the virus in the wastewater of the zones would make it possible to identify the parts of a city where the virus does not circulate, where it is therefore useless to test the population.

But for Dr Blanchecotte, the answer is the same: “there are not 65 million tests available today in France, even adding the antigenic tests which have just been ordered.

As for the PCR self-tests, I doubt that everyone can insert the swab at the back of the nose properly to obtain a reliable result!

"In addition," screening by pooling is not currently authorized, and it would not be useful to resort to it anyway because the positivity rates are too high, adds Stéphanie Haïm-Boukobza.

I don't know what additional levers we could activate.

Except to imagine a partial deconfinement as people are tested.

But in practice, such a device would raise a lot of questions and set up difficulties ”.

Because if the confinement has barely started, "the question today is: what will we do on December 2 for deconfinement?"

“Asks Dr. Blanchecotte.

For him as for Catherine Hill and Stéphanie Haïm-Boukobza, it will be a very sensitive moment "that we must anticipate now".

“In May, screening was not really anticipated in the deconfinement plan, even if things had gone well, observes Stéphanie Haïm-Boukobza.

We will therefore have to see what the needs are at the beginning of December ”.

For Catherine Hill, "without screening the entire population, it is certain that with deconfinement, the epidemic will start again".

It remains to be seen what strategy Jean Castex will adopt who, before being appointed Prime Minister, had been chosen by Emmanuel Macron to prepare for the deconfinement of May.

The executive has until December 1, the last day of confinement (except renewal), to think about it.

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• Screening

• Health

• epidemic

• Coronavirus

• Covid 19

• Confinement