France is not immune to the progression of the Delta variant, which, over other viral strains, could gain the upper hand. Last week, this mutant initially discovered in India, even more contagious than its cousin Alpha, discovered in England, accounted for around 10% of new infections. The proportion doubled this week, according to the Minister of Health, Olivier Véran.
“We can predict that at this speed it will become the majority by the end of July. Each case should now be considered potentially infected with the Delta variant. We must therefore do the maximum in terms of tracing and isolating each positive person ”, estimates epidemiologist Renaud Piarroux. With the epidemic control measures recently lifted in France in view of the significant decline in viral circulation – below 5,000 cases per day – the “test-tracer-isolate” (TTI) triptych remains a significant lever for the fight against the virus. « Under current conditions, the TTI is both more feasible, since there are fewer cases, and more complicated, because people have slightly lowered their guard in terms of barrier gestures, resumed the festivities … One person has more of opportunities to be contaminated and to infect others. Suddenly, it becomes more difficult to trace the contacts of a positive person ”, explains Professor Piarroux, who specifies that the lower the number of cases to follow, the more effective the TTI.
A data which has led to strengthening, since Thursday, the device by generalizing on the territory the retro-tracing. In addition to identifying the contact cases of a person positive for Covid-19, this method must further trace the chains of contamination, taking into account the ten days preceding the identification of the disease. We thus try to go back to the source of the infection by trying to determine where it took place, to find the people present at the same time, their contacts, and to invite them to test themselves.
While the system allows more cases to be found, the system is not necessarily applicable in all situations. “If we try to determine the place of contamination of a person who has, for example, been around bars, it may be complicated”, underlines Renaud Piarroux. Another constraint: epidemic levels must remain very low. “This device is only effective below a circulation threshold which corresponds to roughly 5,000 cases per day”, tells AFP Thomas Fatôme, director general of the National Health Insurance Fund, responsible for monitoring positive cases.
Race against time
An epidemic rebound under the yoke of the Delta variant could thus weaken the device. There remains the vaccination. “The number of new cases being very low, it is almost only thanks to her that the immunization progresses, continues Renaud Piarroux. On the tracing, we are already making great efforts and it is all the more complicated as the virus circulates particularly among younger populations, more mobile and not yet vaccinated. The TTI allows France to do better than some of its neighbors, but the end of the tunnel is vaccination. “
To date, 32.5% of the eligible population has full immunization coverage. According to models from the Institut Pasteur, if a dominant variant has a reproduction rate of four (an infected person infects an average of four), and with « vaccination coverage of 30% in 12-17 year olds, 70% in 18-59 year olds and 90% in over 60 year olds, a peak in hospitalizations similar to that of autumn 2020 could be observed in the absence of control measures ”. The race against time, not yet won, promises to be long.
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