It is a bit like this little black cloud on the horizon, the one we fear does not bode well and which clashes in the middle of an azure sky. While in recent weeks the situation has returned to calm on the front lines of the Covid-19 epidemic, the fear of an epidemic rebound carried by the Delta variant, more contagious, is setting in. In the Landes, it already represents 70% of positive tests. In the rest of France, as in Ile-de-France, it is currently evaluated at 10%. But could very quickly become the majority.
“When a strain of a virus is more contagious, it replaces the previous one”
After peaking at the end of winter, the incidence rate of the epidemic in Ile-de-France has returned to a level equivalent to that of the beginning of August 2020 (31.4%) even though the number of tests is much higher. Consequence: the positivity rate has never been so low (0.9%). But among these rare positive tests, 10% of people infected are now infected with the Delta variant, formerly nicknamed “Indian”. Where there was barely 2-4% a month ago. “This is absolutely nothing abnormal, analyzes Dr. Frédéric Adnet, head of the emergency department at the Avicenne hospital in Bobigny. When a strain of a virus is more contagious, it replaces the previous one. This is the case with all viruses and this is what happened to the British variant at the start of the year. “
In his eyes, as in those of many experts, it is now a matter of weeks, perhaps even days, before the Delta variant dethrones the British variant. “According to a British study, the incidence doubling time is 11 days with the Delta variant”, continues the practitioner. With 10% of cases detected to date, the 50% mark could be crossed in a month. Even before. According to the Regional Health Agency, it is indeed very likely that the figure of 10% is underestimated due to a change in the screening method.
Regional differences
Until the beginning of June, the laboratories looked for, among the positive tests, the main variants in circulation: British, South African, Brazilian … “Today, we no longer focus specifically on these variants because they have sometimes themselves mutated but rather what are called “mutations of interest”, that is to say those which can have an impact on immunity “, explains Dr Laurent Kbaier, biologist at the Biogroup laboratory, which performs half of the PCR tests in Ile-de-France. But if this new screening method is faster, its deployment can disrupt data feedback, estimates the ARS, which expects, in the coming days, to catch up.
At the regional level already, the situation is far from being homogeneous: according to the data collected by the Biogroup laboratory, this variant already affects 17% of cases in Yvelines, 13% in Seine-Saint-Denis or in Hauts-de. -Seine… against barely 4% in Val-de-Marne or Val-d’Oise. “We have observed this type of difference at the arrival of each variant which ends up smoothing out”, analyzes Dr Laurent Kbaier, who recalls that due to the low number of cases, a cluster can boost the results.
Towards a fourth wave?
Therefore, is a fourth wave inevitable? In Britain, the last stage of the deconfinement plan has been postponed to cope with the epidemic resumption: in the last week alone, the number of new cases has increased by 40%. “The epidemic rebound is inevitable but not necessarily the overload of hospital services,” specifies Frédéric Adnet. Vaccination is indeed 95% effective against severe forms of Covid-19, regardless of the variant. People who are vaccinated and who nevertheless contract the virus usually have asymptomatic or mild forms. Proof of this is across the Channel where the hospital services have not seen a massive influx of patients.
“These figures are encouraging, but people must continue the vaccination effort,” insists within the ARS. And in recent weeks, the decline is significant. 46.58% of Ile-de-France residents have received at least one dose of vaccine but the number of first doses is only increasing by 5% per week. However, collective immunity can only be achieved if 70% to 80% of the population is vaccinated.