A Danish study on the BA.2 subvariant, published on January 31, 2022, indicates that, according to the first data, the new mutation is one and a half times more contagious than Omicron. Nothing indicates, for the moment, that it would be more virulent than its big brother.
Is the Omicron sub-variant a new threat to the world? In his latest press release, the Danish Infectious Diseases Control Authority (SSI) looks back on the study on the BA.2 subvariant released on January 31, which she conducted jointly with scientists from the University of Copenhagen, Statistics Denmark and the Technical University of Denmark. Two things stand out in particular from this study. Already, that the rapid spread of the BA.2 subvariant “could be related to an inherent increased transmissibility of the subvariant”.
Is the BA.2 variant more contagious?
This contagiousness is, according to the results of the study, higher than that of the BA.1 variant (ie the Omicron variant as it was known until now). Additionally, if someone in your household is infected with the BA.2 subvariant, “there is a 39% overall risk that another member of the household will be infected within the first week.” For comparison, if someone in your household is infected with BA.1, this risk drops to “29%”. “The risk of being infected was higher in unvaccinated persons than in vaccinated and booster-vaccinated household members in households infected with BA.2 and BA.1, highlighting a positive effect of vaccination against both variants of Omicron”, also points out the study.
It also emerges from this study that “there is evidence in support of the immune evasion properties of the BA.2 sub-variant”. On the other hand, the study does not highlight at any time a greater virulence of the BA.2 sub-variant compared to the Omicron variant. If it covered 17,945 people (for a total of 8,541 households) between December 20, 2021 and January 18, 2022, it must still be “peer-reviewed”, reminds the Danish Infectious Diseases Control Authority to the end of his statement.
As a reminder, BA.2 is a sub-variant of Omicron, a mutation itself divided into three sub-lineages (BA.1, or Omicron as we know it, BA.2 and BA.3). This is why it has many similarities with the mutation first spotted in South Africa, and is difficult to identify. The BA.2 mutation has focused the attention of France and the world for several days, while the peak of the Omicron wave, initially expected for mid-January, has still not been crossed and the number new daily infections regularly break records. The first results of the sequencing of the mutation revealed many similarities between the BA.2 and Omicron variants but also a notable difference on the Spike protein which determines the contagiousness of the virus but also the effects of the immune response enabled by the antibodies. Among these peculiarities, one could prevent “human cells [de] to acknowledge [le variant], even though they would have already been exposed to the Omicron variant”, according to the explanations of Olivier Véran. These first elements of response suggest that the contagiousness of the sub-variant is greater. “BA.2 seems to be transmitted more easily” , confirmed Troels Lillebaek, the Danish epidemiologist and director of the Statens Serum Institut, on BFM TV.
But the real question surrounding the BA.2 mutation “is to know how serious it will be”, insisted Jean-François Delfraissy, president of the Scientific Council, on France info, also on January 25. Studies are continuing to better understand this sub-variant of Omicron and its characteristics.
When did the BA.2 variant appear?
The BA.2 subvariant is an evolved form of the BA.1 mutation commonly referred to as Omicron. If the oldest genomic sequence of Omicron dates from October 25, 2021, that of BA.2 only appeared a week later, on November 1. Despite this sequencing, the submutation was only really identified on December 7 and it took even longer before it reproduced on a large scale, to the point of becoming the majority in Denmark. The Nordic country is the one where the BA.2 variant circulates the most. It already accounts for 66% of Covid-19 cases. The mutation spread like wildfire in just a few weeks, it accounted for 20% of all Covid-19 cases in Denmark during the week of December 27 to January 2, and 45% during the week from January 10 to 16, according to data from the Statens Serum Institut.
Does the BA.2 variant circulate in France?
Coming from Omicron, the BA.2 mutation is likely to spread in France. As of January 25, only 60 contaminations were due to the new variant according to the Minister of Health. In reality, it is impossible to count the number of cases of BA.2 because “the detection of mutations of the SARS-CoV-2 by screening does not allow, in most laboratories, to distinguish BA.1 from BA.2 “explained the biologist Florence Débarre, at the World. It would be necessary to modify the targets of the screenings or to sequence the entire viral genome to identify the nature of the variant, but “the reporting of sequencing data in France is not immediate”.
What are the differences between the BA.2 variant and Omicron?
The Omicron variants, or BA.1, and BA.2 belong to the same family of mutations, BA.2 would even be an evolution of Omicron. Essentially the two mutations are similar but the virologist Etienne Decroly noticed that “BA.2 carries fewer mutations than BA.1, in particular on the Spike protein”. The Spike protein is particularly watched since it concentrates the characteristics linked to contagiousness and the triggering of an immune response. In detail, the scientist explains that on the “furin cleavage site” and the RBD (receptor binding domain) site, which respectively affect the virus’s ability to infect human cells and trigger a neutralizing antibody response, no significant difference of BA.2 compared to Omicron is to be noted. On the other hand, on the NTD domain, “N-terminal domain”, plays a role in the activation of neutralizing antibodies, notable differences have been identified and suggest that antibodies created to fight against Omicron would not be able to bring an immune response against the BA.2 variant. In other words, a person already infected with Omicron could still be infected with the BA.2 sub-variant.
If the risk of being infected with the BA.2 variant exists even after contamination with Omicron, the mutation would not be the cause of a serious form. As with its elder, BA.2 could therefore be more contagious but less dangerous and send fewer patients to hospital. The director of the Danish research institute, Troels Lillebaek, indicated on BFMTV: “Preliminary indicators show that there is no difference between BA.1 and BA.2 for hospitalizations, that there is no no more virulent”.