Increased sequencing, improved tracing, more coercive isolation: is France now equipped to “track the virus”, as the government promises, and avoid a fourth wave of Covid-19 due to the Delta variant?
It is the most effective bulwark, but “the vaccine strategy alone is not enough” to avoid “waves or a too important rebound”, warns the epidemiologist Antoine Flahault, director of the Institute of global health at the university from Geneva.
With a Delta variant considered to be 40% to 80% more contagious than the Alpha, “the level of requirement for minimum vaccination coverage is higher than what was initially thought,” he told AFP. It would take “85% of people immunized for the epidemic to stop”, assesses Pascal Crépey, researcher in biostatistics at EHESP.
For now, only a third of the population is fully vaccinated in France and the government expects 35 million people at the end of August, or 52%. It is therefore necessary “to couple vaccination with a strategy of minimal circulation of the very offensive virus”, pleads Professor Flahault. The good news is that France is “better armed” than last summer to prevent the fall wave scenario from repeating itself.
Play on the summer upturn
The ebb of the epidemic is restoring the effectiveness of traditional measures (screening, tracing, isolation), which are overwhelmed when tens of thousands of new cases are detected every day.
President Emmanuel Macron mentioned in November a threshold of 5,000 cases per day, below which it is possible to quickly identify the patients and their contacts. This winter, the target was not met, but it is now. Last week, the country even fell below 2,000 new cases on average every day. “It is no longer the virus that stalks us, it is us who stalk it”, recently assured the Minister of Health, Olivier Véran, in the Journal du dimanche.
Strengthening the system “test-trace-isolate” must make it possible to respond to the risk represented by reopening and summer relaxation, explains the Ministry of Health. These weeks of calm “allow a transfer of competence from citizens to the health authorities”, judge Antoine Flahault.
When the virus flares up, individuals have the fate of the epidemic “in their hands”, limiting their interactions and respecting barrier gestures. But in a period of ebb, it is up to the government to “regain control, leaving the citizens free”.
Self-tests and saliva tests, presented as complementary tools to PCR and antigen tests, got off to a slow start. Many pharmacists note that the former have not found their audience, while the latter, mostly carried out as part of screening campaigns in schools, have never exceeded 300,000 per week, and are in sharp decline.
Olivier Véran promised free self-tests this summer, with 7.5 million kits distributed on vacation routes, resorts, leisure centers and to vulnerable groups.
Despite the summer recklessness, “when people have symptoms, even colds, not even very specific, they should not hesitate to be tested quickly”, encouraged epidemiologist Dominique Costagliola on Public Senate.
And at the start of the school year, the stake will be “the massive screening at school level, because we know that it is in this “unvaccinated” population that the virus will run, “said the President of the Scientific Council Jean-François Delfraissy on France Inter.
Virus sequencing makes it possible to identify variants and to know how they circulate. Initially considered to be largely insufficient, the public sequencing capacities, dispersed over four specialized platforms and several hospital laboratories, have been progressively reinforced and coordinated, within a consortium.
Since its launch at the end of January, 79,011 positive samples have been sequenced, against around 2,000 sequences in 2020, or “a very significant jump in a short time,” said Yazdan Yazdanpanah, director of the ANRS-MIE agency. However, we are still far from the objective of 10,000 sequences per week an announced time.
Private laboratories will be associated with this effort and should soon make it possible to “double the capacities of the four public platforms”, according to Public Health France. But the name of the selected laboratories will only be known “around July 27”. A “painful childbirth” which wasted precious time, judge with AFP François Blanchecotte, president of the Union of biologists, which represents the private sector.
For Bruno Lina, head of the National Reference Center for Respiratory Viruses in Lyon, “volume is not everything”. The challenge is above all to “be able to shed light on what the emergence of variants means and to be able to detect” the new ones. “The sequencing must be systematic”, considers on the other hand Antoine Flahault, according to whom it can “help the tracing of the contaminations”.
The decrease in the number of contaminations has enabled the Health Insurance to implement another measure recommended for a long time: in parallel with the classic tracing of contact cases, its teams will generalize retrospective tracing, practiced in particular in Japan.
Positive patients had so far been questioned about their contacts going back 48 hours for symptomatic and 7 days for asymptomatic, to identify people they could have infected.
From now on the questionnaire also covers the 10 days before their test, to identify “the reasons, the elements or the moments of contamination, more or less collective, which could have been the source of this contamination”, describes Pierre Rousseau, director general of the CPAM of Loire-Atlantique.
With this technique, “you increase your chances of identifying” contaminated people “that you missed with the classic tracing” and of identifying “super-propagation events”, explains Samuel Alizon, biologist at the CNRS to AFP. , specialist in the modeling of infectious diseases.
Indeed, only 10% of people infected with the coronavirus will infect two or more people. “It is these people”, sometimes called superpropagators, “who are the engines of the epidemic and who must be found,” abounds Antoine Flahault.
Isolation and border control
Since the emergence of the Beta, Gamma and Delta variants, the authorities have tightened the conditions of isolation, gradually implementing a mandatory quarantine for travelers from countries at risk.
When this measure was extended to the United Kingdom at the end of May, it was however specified that “the system of systematic home checks will not be applied to them”. Doctors and elected officials have also criticized the possibility of people in solitary confinement going out at certain times of the day.
Asked about the advisability of drastically restricting flights with the countries concerned, Professor Delfraissy felt that it was “already too late” to hope to prevent the progression of the Delta variant in this way.
Regarding the positive cases of this variant on the territory, the Minister of Health announced on June 20 a “more coercive” framework, with the possibility for the prefects to take quarantine measures for those who would not respond to the tracing teams. or fail to follow the recommendations.