11:15 a.m., March 20, 2022
This barbaric code name, BA.2, designates the new enemy of spring. the sub-variant of Omicron, which replaced BA.1
in Denmark and then in the United Kingdom, is partly responsible for the current epidemic rebound in France. Its spread worries in the United States.
Why does he have such a weird name?
Omicron, a worrying variant according to the qualification of the World Health Organization (WHO), is in fact a generic term which designates without distinction several lineages of very similar viruses. In France, BA.2 has just replaced its “older brother” BA.1, hegemonic until February. “The differences between BA.1 and BA.2 are much less important than between the latter and the variants that preceded them, Delta or Alpha, decodes the virologist and member of the scientific council Bruno Lina. This is why the WHO does not consider BA.2 as a new variant and has not baptized it with a letter of the Greek alphabet. »
Is it more transmissible than BA.1?
Fortunately, it is not more aggressive, but it is undoubtedly more contagious. This increased capacity to infect us explains why it is today responsible for more than 75% of contaminations in France. “Two studies, one Danish, the other English, make it possible to estimate the increase in transmissibility between BA.1 and BA.2 at 30%”, notes the professor of infectiology and member of the Academy of Medicine Anne-Claude Crémieux. At the end of January, the Danish Infectious Diseases Control Authority summarized the Danish study as follows: “If someone in your household is infected with BA.2, there is a 39% overall risk that another member of the household will be infected within the first week. On the other hand, if the person is infected with BA.1, the risk is 29%. »
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The most contagious variant of the Sars-CoV-2 virus we have seen so far
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According to the experts, BA.2 has, like BA.1, facilities for spreading in people who are already immunized but it does not have additional immune escape capacities. Simply, he is ” faster “ than the BA.1 subvariant, in the words of Professor Lina. “He passes more quickly from one person to another”, agrees Professor Crémieux, noting that the interval between the onset of symptoms in an infected person and their appearance in a contact case is reduced by almost half a day compared to BA.1 (about 3.3 days against 3 ,7). These characteristics led WHO expert Maria Van Kerkhove to say on Wednesday that BA.2 was “the most contagious variant of the Sars-CoV-2 virus that we have seen so far”. Eight mutations, carried by BA.2 and not found on BA.1, could be at the origin of the performance of this sprinter.
Does it reduce the effectiveness of the mask?
Here is a fear uttered in a low voice by some experts and which concerns BA.2 today like BA.1 yesterday: Omicron, the champion of contagion, would make the surgical mask a little less effective. This is particularly the point of view of professor of immunology Cecil Czerkinsky. Currently in South Korea, this researcher notes that “despite perfect discipline (wearing a mask, physical distancing, hygiene, etc.) and higher vaccination coverage than in European and North American countries”, contamination is breaking records. “ We are dealing with a “new” virus, much more contagious and transmissible, not only by droplets but also by aerosol. » His recommendation? “Ventilation will become decisive. »
Read also – Covid-19: why the epidemic is still rebounding
“The mask alone is insufficient against Omicron, acknowledges virologist Bruno Lina. Wearing a mask is a risk reduction. » For her part, Anne-Claude Crémieux ensures that “Wearing a surgical mask in an enclosed space reduces the risk of becoming infected by two thirds” and that it provides protection “effective against all variants”. And to assert: “Vaccination provides imperfect protection against infections, and wearing a mask is essential if you don’t want to be contaminated. »
Can it defeat current vaccines?
That was the good news of the past few weeks. Despite the arrival of Omicron, current vaccines remain protective against severe forms of Covid-19. However, their performance declines after four months in the elderly, who must urgently receive a third injection if not already done, and even a fourth dose
if the recall dates back to the fall. Protection against infection (a 45 to 50% risk reduction ten weeks after the third dose) remains unchanged between BA.1 and BA.2, according to the latest weekly bulletin from the British Health Security Agency .