11:30 p.m., July 31, 2021
When did you “meet” the Delta variant?
This variant, which appeared in India at the end of 2020, has been under surveillance since April. At the time, the Alpha virus, known as English, ravaged this country, but three new variants from the same line were associated with a strong outbreak in the Bombay region. The one who gave the impression of gaining the upper hand in this area was not the current Delta variant but one of his two cousins, now very much in the minority. The emergence of variants always takes place in countries where the epidemic is on the rise: in India for the Delta, in South Africa for Beta or in Brazil for Gamma. The latter sparked fears this winter because it appeared to be able to partially escape the immunity conferred by an infection or a vaccine. Finally, for the moment, it has remained confined to South America, with a very minor circulation in Europe.
How did he get to Europe?
Delta entered the UK through travelers from India – a few cases were reported in France around the same time. Initially, it was transmitted within the Indian community, which experiences living conditions more conducive to rapid transmission than the average British population: promiscuity, cramped housing, economic difficulties. And then the virus spread to the whole of the United Kingdom, before arriving here.
Why does it now dominate in France and in Europe?
Two main factors explain this. First, its intrinsic properties: it is 60% more transmissible than the alpha variant, itself 50% more contagious than the original strain. He won the race because he does better than the others: all successful variants have competitive advantages. Secondly, it found a favorable epidemiological breeding ground with us at the beginning of the summer, at a time when its competitors, and in particular the Alpha variant, were ebbing. It is always easier for a virus to enter a population when the previous wave ends.
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Wearing a mask and barrier gestures remain essential elements in the prevention of transmission
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Do its changes explain its competitive advantage?
The Delta variant has at least 13 mutations compared to the Wuhan strain, but sometimes it can carry 15 or 17. Among the mutations located on the spike protein, the key that allows the Sars-CoV-2 virus to enter the cells, two seem to have a particular impact. The first, L452R, was already present on the Henri-Mondor variant, which we identified at the CHU de Créteil. The second, called P681R, appears to increase the virus’s ability to infect cells. It is probably the combination of these two changes that gives it a competitive advantage. When more virus is produced, there are more infected particles in the postilions or the surrounding air and those around infected people are more likely to be infected. For the Delta variant, we estimate the reproduction rate R0, i.e. the number of people infected by a positive case in the absence of any barrier or social distancing measure, at approximately 6, which is equivalent to that of chickenpox. At the start of the epidemic in 2020, it was estimated for the original variant to be around 2.5.
What is Delta’s place compared to other strains?
Delta now has an 80% -90% majority. The situation is likely to remain largely unchanged for the next few weeks. In this context, the interest is not to know if it will soon represent 95% of the samples analyzed but to observe a possible inflection, such as the emergence of a new strain or the progression of another known variant. because that could influence the evolution of the epidemic situation. On the other hand, knowing that an individual is infected with Delta or another has no interest in health care. The patient will be treated in exactly the same way regardless of the variant causing his disease.
Are you worried about the current decline in compliance with barrier gestures, given Delta’s increased contagiousness?
In the midst of the epidemic outbreak of this highly contagious variant, wearing a mask and barrier gestures remain essential elements in the prevention of transmission, in addition to vaccination which, to date, has only affected a little more than half of the French population. Vaccinated people are well protected against severe forms of the disease, but some of them can become infected, have a mild form of the disease and transmit the infection for a short time.
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There is currently no argument to believe that Covid-19 is more or less severe with this or that variant
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Should we be concerned that vaccines are an imperfect shield against the transmission of Delta, as the American authorities have just assured?
A vaccinated person who catches the virus will usually have very little symptoms and very short duration, with much less chance of transmitting the disease than an unvaccinated sick person. The number of vaccinated people who are at risk of developing a severe form of the disease is very small, as the vaccines are 90-95% effective. These are mainly people who are very old or have a weakened immune system. It is for them that we are considering a third booster dose. Of course, we do not yet have all the data showing that a booster is essential, but the precautionary principle suggests that it should be done at the start of the school year to boost their immune response.
Is Delta more dangerous than the previous strains?
There is currently no argument to believe that Covid-19 is more or less severe with this or that variant, including Delta. The results of the studies can be biased by the epidemiological characteristics of the different outbreaks, which do not always affect the same audiences and have different time frames. The extension of vaccination will also dramatically change the presentation of the disease.
Jean-François Delfraissy had spoken of an “epidemic within the epidemic” concerning the Alpha variant. Could the same be said of the Delta?
No, it was not for the Alpha variant – and it is not for the Delta – a new epidemic, but the natural evolution of the original epidemic. The expression wrongly feeds a certain catastrophism. The current rebound due to the Delta variant is part of the series of successive waves of the pandemic phenomenon. All is not dark: we are moving from a first pandemic phase, during which the virus spread very quickly on the surface of the Earth, to an endemic phase, which will probably be characterized by regular flare-ups. The most vaccinated regions will be less affected than the others. We are going to live with this virus as we have lived for centuries with other respiratory viruses.
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The natural evolution of viruses is towards a greater efficiency of propagation, in particular when herd immunity is reinforced.
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We laymen in biology, we would be afraid for nothing by focusing on the variants?
All respiratory viruses mutate, but we had never looked at them so closely! The tools to do this did not exist. Today, thanks to the health crisis, the genetic sequencing radar to follow the evolution of epidemics has grown. The techniques, they, had fortunately made a spectacular leap in recent years. Mutations, we were only interested in chronic diseases like HIV or hepatitis C because they make viruses resistant to antiviral treatment, but not for acute infections of this kind. Perhaps this work on Covid-19 will help change our outlook on other respiratory viral infections. For example, each year, between 5,000 and 15,000 people die indifferently from complications of the flu.
Could an even more contagious variant emerge?
Yes of course. The natural evolution of viruses is towards a greater efficiency of propagation, in particular when herd immunity is reinforced. The virus is struggling to survive and to continue to spread as efficiently as possible. In general, this better spreading efficiency is accompanied by a gradual reduction over the years of the symptoms of the disease. This is undoubtedly what has happened with other respiratory infections that have been present for centuries and today are the source of mild illnesses in humans.
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