• In a few weeks, the Delta variant has established itself in France, where it represents the majority of new cases and causes an outbreak of contaminations.

  • This variant is more contagious than the original strain of the coronavirus, but also more than the Alpha variant, the majority in France before it.

  • In addition, the Delta variant has a shorter incubation period and less suggestive symptoms.

    A cocktail favoring the increase in contamination.

An exponential progression.

Still little present in France at the end of May, the Delta variant today represents the majority of new contaminations, which it has exploded in recent days due to its greater contagiousness.

In 24 hours, the number of new Covid-19 contaminations climbed to 18,000, against less than 7,000 a week earlier, the Minister of Health, Olivier Véran, alarmed on Tuesday, according to whom this increase, due to the Delta variant, is unpublished.

But how to explain this outbreak?

A lightning spread

Nearly 20,000 new contaminations in twenty-four hours, “this means that we have an increase in the circulation of the virus of the order of 150% over a week: we have never known this, nor with [the historical strain of] Covid, neither with the English variant, nor with the South African nor with the Brazilian ”, noted the Minister of Health.

Flash propagation, this is how we could summarize the progression of the Delta in France in a few weeks. While it is only present in 0.2% of samples taken during the Flash survey of Public Health France (SpF) on May 11, in the following survey of May 25, it represents 1% of cases. Then everything gets carried away: "Currently in France, 2 to 4% of the positive tests that we screen correspond to the Indian variant", declares Olivier Véran on June 15. A week later, it represents "between 9 and 10%" of new cases, says government spokesman Gabriel Attal. And on July 9, Olivier Véran warns: the Delta variant "is gradually replacing all the other strains of the coronavirus that existed and it will soon be in the majority, probably this weekend, in our country".

This is the case today: “the Delta variant (was) detected in 55% of the confirmed cases sequenced in (the last) Flash survey, confirms SpF in its latest epidemiological bulletin.

It is now the majority in metropolitan France ”.

And it "continues its rapid progress in Europe and at the global level, now affecting more than a hundred countries," she adds in her risk analysis on the variants of Covid-19, carried out jointly with the National Reference Center respiratory viruses on July 15.

In the most affected countries, there is an increase in cases and hospitalizations, more or less important depending on the country, in particular in the United Kingdom, Portugal, Russia ”or even India.

Shorter incubation period and 1,260 times higher viral load

How to explain the lightning speed at which the Delta variant spreads? It "is characterized by increased competitiveness compared to other variants, in particular the Alpha variant, and it is likely that it is already the majority worldwide or is in the process of becoming so", assures Public Health France. In question: its higher transmissibility, “approximately 2 times higher” than “the historical viruses and than the variants Alpha (approximately 40 to 60% more transmissible), Beta (approximately 60%) and Gamma (approximately 30%)”.

Cherry on the Covid: with the Delta variant, an infected person would be contagious two days earlier than with other strains, according to the findings of a study conducted by researchers at the Guangzhou Center for Disease Control and Prevention in China , pre-published on the medRxiv site a few days ago. By performing daily PCR tests on a sample of people infected with Delta, the researchers determined that the incubation period, from 6 days on average with the historical strain, was shortened with the Delta variant, to 4 days between exposure to the virus and the appearance of the first symptoms. They also discovered that with this variant, patients had a viral load "1,260 times higher" than the first strain,suggesting that this variant is "much more infectious at the early stage of infection". In short: it causes hidden contaminations before the appearance of the first symptoms. What to explain the global explosion.

Less suggestive symptoms

Additional explanation for this epidemic outbreak: the Delta variant is manifested by a symptomatology a little different from the previous strains.

According to data from the Zoe Covid Symptom study conducted by researchers at King's College London, headache, sore throat and runny nose, fever and cough are the symptoms most commonly described by people infected with the Delta variant.

With it, the loss of taste or smell is rarer.

And in younger people, in whom the variant is on the rise, the disease often looks like a simple cold or gastroenteritis.

Not very serious symptoms in this age group which continues its social activities, favoring the spread of the variant, which can be more serious if it infects more fragile people.

While nothing indicates, for the time being, an increased lethality compared to other strains, "preliminary data suggest an increased risk of hospitalization and severe forms related to this variant compared to the Alpha variant", observes Public Health France, which insists on the interest of anti-Covid vaccination. “In the event of a complete vaccination schedule, the efficacy of the Pfizer and AstraZeneca vaccines against this variant remains high against the symptomatic forms and very high against the severe forms. However, the efficacy of these vaccines is limited after a single dose, which is a strong incentive to intensify vaccination, ”insists the health agency.

Risks which pushed the Head of State to extend the health pass, with the aim - successful - of convincing French people who had hitherto been hesitant or reluctant to take the leap of vaccination.

In a few days, more than 5 million appointments were made on online reservation platforms.


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