Between November 2020 and January 2021, the world got to know the variants of the coronavirus. A new critical phase in the epidemic then begins. In a few weeks, the English, Indian, South African and Brazilian variants are particularly sequenced and worry the health authorities: more contagious, more lethal, making vaccines less effective … Each has its own characteristics, but each time the observation is the even: they are more dangerous than the original strain.
The English variant, renamed Alpha variant by the WHO, notably caused a new wave in Europe and devastated the United Kingdom because of its higher contagiousness, before the Indian variant, renamed Delta, did the same for a few more weeks. late. Since then, no other variant has seriously emerged. How to explain this sudden absence? 20 Minutes make the point.
How does a variant form and emerge?
The coronavirus is an RNA virus, a family of viruses much more prone to mutations than the DNA virus, protected by double helices, unlike RNA which is only on a single strand. However, Covid-19 mutates much less than other RNA viruses, such as the “normal” flu.
The coronavirus is at risk of mutating each time it is transmitted. When the mutations are large and cause a major change in the virus, this is called a variant.
Not all variants are necessary. “Mutations are not that rare, but to be an emerging variant, this mutation must bring something more: whether it be on its pathogenic power (virulence: triggering serious forms), its transmissibility, its infectivity ( ability to infect cells / to trigger disease), or its antigenicity (the fact that it can induce an immune response), ”notes Anne Sénequier, doctor and co-director of the Observatory for Global Health.
In the context of the coronavirus, this evolutionary advantage often comes down to greater contagiousness. According to some studies, the Delta variant is 60% more transmissible than the Alpha variant, itself 50 to 74% more transmissible than the original strain of Covid-19.
Take the example of the Alpha variant in the UK. By spreading more quickly, it infected more people, who themselves contaminated more, that is to say always fewer targets for the original strain. As the Alpha variant contaminated more and more, the original strain diffused less and less, to the point of being replaced.
Does Delta’s hyper-contagiousness protect us from other variants?
As we have seen, the Delta variant is extremely contagious, and a variant imposes itself mainly on other strains thanks to this. We can therefore wonder if, due to Delta’s hyper-contagiousness, no other variant manages to transmit itself enough in the face of it and to impose itself.
France can illustrate the point. At the end of May, the country had 85% Alpha variant, 6% Beta variant (the South African variant), a figure that has been stable for months, the rest being occupied by the original strain and the Delta variant. A study by Public Health France on October 13 now shows that almost 100% of tests in France are of the Delta variant. Admittedly, the Alpha variant was replaced as expected, but also the Beta variant. “Today, to be emerging, you have to be at least as transmissible and potentially have another advantage,” concludes Anne Sénequier, which is not so easy against Delta.
Is mass vaccination a possible explanation?
As we have also seen, the more the virus is transmitted, the more likely it is to mutate. However, vaccination decreases both the chances of catching the virus and transmitting it. In conclusion, the more we vaccinate, the less the virus circulates, the less chance it has to mutate.
Global mass vaccination could therefore be another explanation: compared to December 2020, when vaccines did not exist, 48.2% of the population received a first dose on Tuesday and 36.5% are fully vaccinated. . In December 2020, there were 750,000 new cases of coronavirus per day on average in the world, against 410,000 currently, and with more tests than at the time. The virus circulates less, which may also explain the absence of variants.
Variants, end of game?
Be careful not to claim victory too quickly, however. More than half of the population has not received a single dose, and 410,000 new cases a day, that’s still nearly three million a week. “As long as the virus is circulating as much, the risk of a new variant is possible,” warns Anne Sénequier.
On a world population so vaccinated, an evolutionary advantage could precisely be a resistance to the vaccine, raising fears of a violent wave even for countries which think they are out of the woods. “What is certain is that the emergence of a variant resistant to our vaccination may be more important as time passes because it promotes the circulation of the virus”, confirms Anne Sénequier.
One of the solutions for it would therefore be to provide massive doses to the countries of the South, which have received very little vaccination. Thus, the African continent is vaccinated at less than 10% of its 1.3 billion population. A potential nest of variants, which could well make a comeback in the event of too much selfish inertia from the North.