Voici ce qu'il faut savoir sur les variantes de coronavirus les plus courantes et sur l'efficacité des vaccins COVID-19 contre ces souches. </p><div> <p>Seize mois après le début de la pandémie, la moitié de tous les adultes américains ont été vaccinés et le nombre de nouveaux cas quotidiens de coronavirus est tombé en dessous de 30 000 pour la première fois depuis juin.
But infections involving disturbing coronavirus variants continue to emerge. Some of these mutated strains are more transmissible than previous versions of the virus, while others may partially escape antibodies developed in response to previous infections. Concerns therefore persist about the effectiveness of authorized COVID-19 vaccines against these variants.
Earlier this year, laboratory studies exposed blood samples from people vaccinated with the variants first discovered in South Africa and Brazil. The results showed that the samples generated fewer protective antibodies capable of neutralizing these variants than they did when exposed to the original virus.
But as more people get vaccinated, real-world data has started pouring in from areas where these pernicious variants dominate. This provides better insight into the effectiveness of leading injections in preventing symptomatic infections. And the results are promising: None of the variants monitored by the Centers for Disease Control and Prevention and the World Health Organization can completely escape vaccines. In addition, reduced antibody responses did not necessarily translate into less protection against infection.
COVID-19 vaccines even appear to work against a group of variants discovered in India this winter, called B.1.617, which likely contributed to the coronavirus outbreak in the country. UK government data, obtained by the Financial Times, suggests that two doses of Pfizer or AstraZeneca vaccines offer a high degree of protection against B.1.617.
The table below summarizes what we know so far about the effectiveness of five vaccines in protecting people against four of the more worrying coronavirus variants.
Comparison of disturbing variants of the coronavirus
Countless versions of the coronavirus are circulating around the world, each separated by a small number of genetic mutations. Once a multitude of mutations make a particular strain more effective at infecting humans, deadlier, or more able to evade antibodies generated by a vaccine or previous infection, geneticists call it a variant of concern.
There are four, according to the WHO: B.1.1.7, the variant initially found in the UK in September; P.1, which was discovered in December; B.1.351, which was detected in samples from South Africa dating from October; and B.1.617, a group of strains first spotted in India this winter.
The first three share a mutation that affects the shape of the virus’s spike protein, which it uses to invade cells. Perhaps this is why these variants are more heritable.
Studies have shown that the B.1.1.7 variant is 50-70% more contagious than its viral predecessors. Recent evidence also suggests that people infected with this variant have a higher risk of death than those who receive other strains. One potential reason is that people infected with B.1.1.7 tend to have higher viral loads, which means they produce more viral particles when infected.
The same is true for the P.1 variant, which is 40% to 120% more transmissible than previous versions of the virus and possibly more deadly, although more research is needed to confirm this. An April study found that people who contracted COVID-19 in Manaus, Brazil were almost twice as likely to die after P.1 dominated the viral landscape in Brazil. But it is not known whether this higher death rate is related to the variant or to Manaus’ overburdened hospital system. P.1 has been detected in 51 countries.
Variant B.1.351, on the other hand, is estimated to be 50% more transmissible and has been found in 92 countries. But studies haven’t shown it to be more deadly than the original virus.
The variant first found in India, B.1.617, is actually four separate strains, according to the CDC. The fastest spreader of the lot is B.1.617.2, which has spread to 50 countries and is now the dominant form of the virus in the UK. This strain has a combination of mutations that help it bind to cells more tightly and allow it to partially escape antibodies developed in response to infection with the original coronavirus. There is no evidence that these variants are more lethal, but the WHO has said that B.1.617 may be more transmissible.
Vaccines resist variants well
The main hits may still be slightly less effective against the variants than against the original virus, but so far it seems they are still protecting people.
“There’s some degree of reduction in efficacy, but it’s going to be manageable,” John Moore, an immunologist at Weill Cornell Medical College, told STAT. “That’s why we call these ‘concern variants’ and not ‘mass panic variants’. “
However, some shots seem to perform better than others – especially against strains B.1.351 and P.1. A recent study from Qatar found that the Pfizer vaccine is 75% effective in stopping B.1.351 infections in the real world, while the effectiveness of the AstraZeneca vaccine has fallen to 10% in some trials in South Africa. China’s Sinovac vaccine, meanwhile, was found to be around 50% effective in stopping symptomatic COVID-19 in Brazil, where three-quarters of infections were due to the P.1 variant.