SUMMARY :
- BA.2: how many cases in France?
- What symptoms?
- Contagion: what do we know about BA.2?
- Is BA.2 more severe than BA.1?
- What are the differences between BA.1 and BA.2?
- How is BA.2 monitored in France?
The Minister of Health, Olivier Véran, reported this Friday March 11 of a “rebound” of the Covid-19 epidemic “in France and in the countries which surround us”. “The Covid is no longer falling, it is even increasing,” explained the minister. “On the other hand, the hospital load continues to drop but the pace of this decrease has started to slow down, so we are extremely vigilant”.
While almost all health measures (vaccination pass, indoor mask, company and school protocol) will be lifted this Monday, March 14, Olivier Véran asked fragile people to be vigilant.
BA.2: how many cases in France?
According to Public Health France (newsletter of March 10), the BA.2 sub-lineage is now the majority in France : 52% the last week of February (week 9), 43% in week 8, 25% in week 7, and 15.4% in week 6.
As a reminder, 4Omicron sub-lineages (variant which represents 99.9% of cases detected in France) have been defined: BA.1 (and its sub-lineage BA.1.1), BA.2 and BA.3. BA.2 is therefore taking the place of BA.1. “The BA.1 and BA.1.1 sub-lineages represented 22% and 34% of the Omicron sequences of Flash S08”, specifies SPF.
What symptoms?
At this stage, symptoms which appear following an infection by BA.2 seem identical to those felt with BA.1. In short, these are the Omicron symptoms.
Contagion: what do we know about BA.2?
Questioned by Europe 1 on Sunday March 6, epidemiologist Antoine Flahault explained that this BA.2 sub-variant of Omicron “is more different from BA1 than BA1 was different from Delta” and that it could “play extra time”, while an epidemic recovery is currently observed in Europe, in Germany, Switzerland and Austria in particular. hong kong is also experiencing an “unprecedented” rise in cases, due to BA.2 and globally Asia and the Pacific, relatively spared so far, are facing a strong epidemic wave, he added.
According to the epidemiologist, “the small fear that we can have is that having been infected with BA.1 in January, one can again be infected with BA.2 and have a new wave.”
the sub-variant BA.2 is more contagious than the original Omicron BA.1 : this is the conclusion from a Danish study in pre-publication covering 18,000 people between December 20 and January 18. In Denmark, this variant became the majority from the end of January.
“If someone in your household is infected with BA.2, there is a 39% overall risk that another household member will be infected within the first week. In contrast, if the person is infected with BA.1, the risk is 29%,” said the Danish Infectious Diseases Control Authority (SSI) in the press release published on January 31 and relayed by AFP. In other words, BA.2 is one and a half times more contagious than BA.1.
Another point of the study: vaccinated people, and in particular those who received a booster, are much less likely to be infected.
Is BA.2 more severe than BA.1?
At this stage, some preliminary analyzes also carried out by the Danish Public Health Agency (SSI) showed no difference between BA.1 and BA.2 in terms of impact on hospitalizations.
Although Denmark has recorded a sharp increase in contamination due to this variant, health restrictions were lifted on February 2. The country considers that on the one hand Omicron (whatever its form) is less severe and on the other hand that the vaccination coverage is sufficient.
For the moment, there is nothing to panic about. Vaccination continues to protect us from severe forms, including BA.2. And in France, vaccination coverage is good: 80% of the total population has received at least one injection (54.2 million people) and 79% of the total population has a complete vaccination schedule (53.3 million people) according to the figures communicated by Santé Publique France on March 8.
In addition, the immunity conferred by successive vaccines and variants makes our immune system increasingly efficient (we speak of cell-mediated immunity).
What are the differences between BA.1 and BA.2?
The variants are distinguished by their genetic identity card. Such variant is different from such other variant because it has X mutations that the other does not have.
And one of the major differences between BA.1 and BA.2 is the fact that BA.1 has the 69-70 deletion which is not the case with BA.2. A deletion is a type of modification of the genome corresponding to the absence of part of the sequence.
Public Health France explains in an article dedicated to BA.2 published on January 25, that it is “normal to observe in a circulating variant a genetic diversification over time and the appearance of new sub-lineages.”
How is BA.2 monitored in France?
In a number of countries including South Africa and the United Kingdom, BA.1 is detected through the use of a method called S-Gene Target Failure (SGTF), the principle of which is to identify the deletion (therefore the part of the gene lost) of BA.1. As BA.2 does not carry this deletion, it is not counted by this method.
In France, the strategy of screening detects all Omicron without distinction, whether BA.1 or BA.2. It is only in a second time that a sequencing is carried out in order to distinguish the two sub-lineages. In short, screening makes it possible to follow the Omicrons as a whole and sequencing allows a more detailed analysis of the different sub-lineages.
Be careful however, the French sequencing system has a drawback: the results are made public two weeks late. We therefore do not know the exact number of people infected with BA.2 in real time. That said, the circulation of BA.2, even if it is progressing, remains weak for the moment.
Sources:
- Weekly update on Public Health France, March 10, 2022.
- Transmission of SARS-CoV-2 Omicron VOC subvariants BA.1 and BA.2: Evidence from Danish HouseholdsJanuary 28, 2022.
- Variant Omicron: what surveillance is in place?, Santé Publique France, 25 January 2022.
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