Covid-19 variants: why a more contagious virus may be worse than a deadlier virus

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The two new strains of Covid-19, detected in the United Kingdom and South Africa, have worried the international community for a few weeks. The reason is simple: they could be transmitted more easily and therefore spread faster. In addition, the two variants could also be more dangerous than the previous strain of the virus.

Since its appearance, the Sars-CoV-2 virus has mutated several times. In recent weeks a first variant has been identified in the UK, more precisely in London, Kent and parts of Essex and Hertfordshire. This strain has grown rapidly and spread across the country and "may be associated with more rapid spread in the south-east of England," British Health Minister Matt Hancock said in front of the House of Commons on December 14. . This new variant is now circulating in various countries of the world.

Another strain of Covid-19 has also been discovered in South Africa. Like the British variant, the latter has been seen in other states.

Are Covid-19 Variants Really More Contagious?

Several hypotheses indicate that the two variants of the virus could be highly transmissible. However, so far, no definitive evidence has proven this. Many continue to wonder about the contagion of these two strains. In a statement, published on December 29, the European Center for Disease Prevention and Control (ECDC) estimated that "a clear link between ACE2 receptor binding (in human cells) and increased transmissibility has not been established, but it is plausible that such a relationship exists. "

British Prime Minister Boris Johnson told a press conference on December 19 that the variant circulating in the UK "is transmitted much more easily." He said that, according to the first data, this variant is "up to 70% more contagious" than the previous strain.

This was confirmed by a study carried out by a team from the London School of Hygiene and Tropical Medicine, whose results were published on December 31 by the Center for Mathematical Modeling of Infectious Diseases (CMMID). The researchers estimated that the variant identified in England is 50 to 74% more contagious (mean value: 56%) than the pre-existing variants of Covid-19.

Variants of Covid-19: Does its higher transmissibility make the virus more dangerous?

Although there is no information indicating that infections by these strains are more serious, due to increased transmissibility, the impact of the coronavirus in terms of hospitalizations and the number of deaths is considered high, in particular for the elderly or those who suffer comorbidities, specifies the European Center for Disease Prevention and Control (ECDC) in its press release.

British epidemiologist Adam Kucharski also explained on Twitter, with a statistical demonstration, that Covid-19 variants are much more dangerous due to their contagion. "Suppose the current R0 (reproduction rate) is 1.1, the risk of death is 0.8%, the generation time (that is, infecting a person after being exposed to the virus) or 6 days and 10,000 people are infected. 129 new deaths would be expected after a month of spread, "he said.

"What if the risk of death increases by 50%? We would expect 193 new deaths. Now suppose that the transmissibility increases by 50%. In this case, we would expect 978 new deaths later." A Sars-CoV-2 variant that is 50% more transmissible would generally be a much bigger problem than a variant that is 50% more lethal, "he wrote on Twitter.

In their study, researchers from the London School of Hygiene and Tropical Medicine also reported that increased transmissibility of the virus is likely to lead to a sharp increase in Covid-19 incidence, hospitalizations and deaths "expected to reach higher levels. in 2021 to those observed in 2020, although the restrictions implemented before December 19. "

"Our estimates suggest that measures similar in severity to the national containment implemented in England are unlikely to reduce the effective number of reproductions," we can read in the study.

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