Omicron BA.2 sub-variant: symptoms, transmission, in France

[Mis à jour le 2 février 2022 à 16h17] BA.2 is a subvariant of Omicron, itself a variant of the Sars-Cov-2 coronavirus. BA.2 is detected at low levels in most northern European countries and from the west. “The epidemic remains particularly strong and the variant BA.2 urges us to be cautious. Many questions still surround this sub-variant of Omicron. It seems that it is even more contagious, that it presents significant risks of recontamination but it does not seem more dangerous than the Omicron variant, it would not cause no more severe forms“ reassured Gabriel Attal during the Council of Ministers on February 2. The Omicron variants identified in France until the second week of January still belong overwhelmingly to the BA.1 sub-lineage. According to the results of the Flash surveys mentioned by Santé Publique France in its epidemiological point of January 27, “the proportion of BA.1 and BA.2 was 68% and 0.26% in S01 (4 BA.2 sequences), 94% and 1% in S02 (9 BA.2 sequences). The spread of the BA.2 sub-lineage in some countries may suggest a advantage of transmissibility compared to BA.1, but preliminary data support a similar severity. The evolution of the proportion of BA.2 and knowledge about this sub-lineage will continue to be closely monitored over the coming weeks.“.”It responds well to the vaccine with respect to the severe forms, the severe forms do not occur in people who have been vaccinated three times. And then it doesn’t seem to be more virulent. There is no description from the Danes of new symptoms” reassured Professor Antoine Flahault, epidemiologist on BFM TV January 21. Today it is majority in Denmark and India. What is this new mutation of Covid-19? Is she more contagious, more dangerous, than Omicron ? the vaccine effective against this new variant? Update on the situation.

Definition: what is the BA.2 sub-variant?

“The BA.2 is a subvariant of Omicron. It is a “little cousin” of the Omicron variant“declared Jean-François Delfraissy, president of the Covid Scientific Council, at the microphone of France info Tuesday, January 25. Named BA.2, it is the youngest of the majority strain of this variant, called BA.1, which is the majority in Europe. The difference between BA.1 and BA.2 is significant, in particular within the Spike protein, specifies Santé Publique France. If discussions are underway to determine whether BA.2 should be considered as a different variant of BA.1, they are both currently grouped within the Omicron variant. A danish study published in January and conducted by the research institute Statens Serum Institut (Copenhagen) pointed out that “the initial analysis does not show no difference in hospitalizations for BA.2 compared to BA.1″. “Worldwide, the Omicron variant represents 94% of circulating viruses with several subtypes: BA.1, BA.2, BA.3 and those not assigned to BA.1-3 lineages. The BA.1 subtype accounts for 90% of circulating variantsand the BA.2 subtype between 3 and 4%. All of these sub-variants seem to have the same characteristics” informs the Covid Scientific Council in its Opinion of January 20.

What is the rate of the BA.2 variant in France?

The BA.2 sub-variant is present in France but remains very much in the minority. “Among the interpretable sequences of the Flash surveys, the proportion of BA.1 and BA.2 was 68% and 0.26% in week 01; 94% and 1% in week 02. Given that 5.2 million new cases of SARS-CoV-2 infections were reported between S52 and S02, the number of infections by BA.2 over this period is estimated at 9,900 vs 3.6 million for BA.1. Diffusion of the BA.2 sublineage in some countries may suggest a transmissibility advantage over BA.1, but preliminary data support similar severity“said Public Health France in its epidemiological update of January 27.

What are the symptoms of the BA.2 subvariant?

For the moment, there are no specific symptoms listed on the few cases of BA.2 sub-variants. In contrast for the Omicron variant “lEpidemiological investigations indicate a specific clinical presentation with more upper respiratory symptoms and less loss of taste and smell, as well as less severity (risk of hospitalization and admission to intensive care up to 80% lower )” reported Public Health France January 26.

Is the BA.2 variant more contagious than Omicron?

“It seems that it is even more contagious (than the Omicron variant, editor’s note), that it presents significant risks of recontamination” declared Gabriel Attal during the Council of Ministers on February 2. “The spread of the BA.2 sub-lineage in some countries may suggest a advantage of transmissibility compared to BA.1, but preliminary data support a similar severity” already informed Professor Antoine Flahault on BFM-TV on January 21. In France, the screening strategy makes it possible to detect all Omicron cases without distinction, whether they are BA.1 or BA.2. “Secondly, the sequencing carried out within the framework of the Emergen Consortium makes it possible to follow the differentiated diffusion of these two sub-lineages” warned Public Health France.

Is the BA.2 variant more dangerous than Omicron?

It seems that it is more contagious, that it presents significant risks of recontamination but it doesn’t seem more dangerous than the Omicron variant, it would not cause no more severe forms“ reassured Gabriel Attal during the Council of Ministers on February 2. “In terms of severity, preliminary data from Denmark showed a equivalent hospitalization rate between BA.1 and BA.2. Preliminary analyzes in the UK showed a higher secondary attack rate for BA.2 compared to BA.1 (13.4% vs 10.3%) but a vaccine efficacy against similar symptomatic infections for the two sublineages. Further studies are underway to more accurately assess the transmissibility, severity, and immune response evasion of BA.2 compared to BA.1.” noted Public Health France. According to the Danish study published in January “from infectivity testing […] are in classincluding attempts to culture BA.2 in order to perform antibody neutralization studies“.”Very early observations in India and Denmark suggest that there is no no major difference in severity compared to BA.1“tweeted Tom Peacock, a virologist at Imperial College London, on January 19, 2022.

Are vaccines effective against the BA.2 variant?

“L’vaccine efficacy is maintained against Omicron after administration of a booster dose, especially against severe forms” confirmed Public Health France on January 26. “It responds well to the vaccine against severe forms, severe forms do not occur in triply vaccinated people“said Pr Antoine Flahault, epidemiologist on BFM-TV on January 21.”It is expected that the vaccines also have an effect against serious diseases when infected with BA.2“had estimated the Danish scientists who are continuing their analyses.

What is the situation in Denmark?

“He [le sous-variant BA.2] seems to have seized power in Denmark” indicated Jean-François Delfraissy on France Info on January 25. According to the results of the Danish study, “the BA.2 variant accounted for 20% of all cases of covid-19 in Denmark in week 52, increasing to about 45% during week 2. During the same period, the relative frequency of BA.1 has dropped“. The situation in Denmark, where the replacement of BA.1 by BA.2 seems to coincide with a rebound in incidence, raises the question of a greater transmissibility of BA.2 compared to BA.1. “However, it is important to note that the country had lifted all the measures in September 2021 and only reintroduced some of them in mid-November 2021” emphasizes Public Health France.

Sources:

– “Risk analysis on emerging variants of SARS-CoV-2”, January 26, 2022, Public Health France.

– COVID-19: epidemiological update of January 27, 2022, Public Health France

-“Now a variant of Omicron, BA.2, accounts for nearly half of all Danish Omicron cases” January 20, 2022, Statens Serum Institut.