Variant Omicron BA.2: 25% in France, reinfection, symptoms

[Mis à jour le 4 mars 2022 à 10h36] BA.2 is a subvariant of Omicronitself a variant of the Sars-Cov-2 coronavirus that appeared in France at the end of 2021.”The BA.2 sub-lineage continues to progress to reach 25% of cases in week 7 (from February 14 to 20) against 15.4% in week 6 (from February 7 to 13). The progression of BA.2 to the detriment of BA.1 is observed in all regions of metropolitan France” indicates Public Health France in its epidemiological point from March 3. “It was became the majority in New Aquitaine since the week of February 14, where it seems to have been introduced earlier than in other regions“adds the organization. If BA.2 seems less dangerous than Omicron, this subvariant is more transferable. BA.2 infection may occur after a first BA.1 infection has revealed a study from the Danish Health Institute in February. One gradual replacement of BA.1 by BA.2 is observed in many countries, especially in Europe. What is this new mutation? of Covid-19? Is it more contagious, more dangerous, than Omicron? the vaccine effective against this new variant? The symptoms are they different? Update.

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, especially within the Spike protein. “The most recent data appear to confirm that BA.1 and BA.2 show similar severity and immune response evasion, and therefore BA.2 is not considered a distinct variant but is included in the Omicron VOC.” specifies Public Health France. A danish study published on January 20, 2022 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″.

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

“The BA.2 sub-lineage continues to progress to reach 25% of cases in week 7 (from February 14 to 20) against 15.4% in week 6 (from February 7 to 13). The progression of BA.2 to the detriment of BA.1 is observed in all regions of metropolitan France” indicates Public Health France in its epidemiological update of March 3. “It was became the majority in New Aquitaine since the week of February 14, where it seems to have been introduced earlier than in other regions“adds the organization.

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. On the other hand for the Omicron variant “epidemiological 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?

“Early data from limited studies suggest that the BA.2 is 30% more transmissible than BA.1. In addition, an analysis of the data shows a growth rate advantage of BA.2 over BA.1 in the 43 countries with sufficient data on the sequences and the co-circulation of the two lineages.“Said the WHO on February 16. “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 Danish study of January 31 reveals “an overall secondary attack rate of 39% in households infected with BA.2vs 29% in households infected with BA.1.”

Is it possible to be re-infected with BA.2 after Omicron?

A BA.2 infection can occur after a first BA.1 infection revealed the Danish study published on Tuesday 22 February. “Researchers studied the number of individuals who had two positive tests and used genome sequencing to look for the variants of the virus with which they had been infected.. The researchers found 67 cases in which the same individual had been infected twice with an interval of 20 to 60 days and where both infections were due to Omicron subtypes“. In 47 of the cases, the affected individual was first infected with BA.1 and then with BA.2. “The majority of those infected were young and unvaccinated, and most had mild symptoms during their infections“. If the original Omicron quickly spread, it is among other things because it can recontaminate people who already have antibodies.“, recalled epidemiologist Catherine Hill, interviewed by Le Figaro January 25. The duration of immunity may therefore depend on the variants, and especially on a new variant, which could circumvent the immunity acquired with infection with another variant. This was the case with Omicron at the end of 2021, which can partially escape protection from infection or the vaccine. And it seems that this is also the case with BA.2, even more contagious. On December 17, a Imperial College London study believed that “the risk of reinfection with the Omicron variant is 5.4 times greater than that of the Delta variant”.

Is the BA.2 variant more dangerous than Omicron?

“Omicron BA2 subvariant does not ’cause a more severe form’ of Covid than BA1” according to Maria Van Kerkhove, technical officer of the WHO on the subject of Covid-19. She indicated that there was no not “difference in terms of severity between BA1 and BA2 and therefore a similar level of severity in terms of risk of hospitalization“.”After adjusting for age, previous infections, gender, or ethnicity, Iand risk of hospitalization and severe form [du Covid-19] with BA.2 (0.87) would be even lower than with BA.1“according to a report published by the British Health Agency. The study focused on the risk of hospitalization defined as admission as an inpatient to the hospital or presentation to emergency care that resulted in admission, transfer or death, after BA.2 compared to BA.1. These results are still preliminary and based on a small number of cases, so “these estimates may change” afterwards. 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.

Are vaccines effective against the BA.2 variant?

“Preliminary results of a negative case-control study conducted in the United Kingdom showed no no difference in vaccine efficacy against symptomatic disease between BA.1 and BA.2more than six months after administration of two doses of the primary series or two weeks after administration of an additional booster dose” says the WHO on February 16. “This suggests that vaccination is at least as effective in preventing acquisition of BA.2 and may be more effective in preventing transmission of BA.2 than BA.1“, remarked the organization. “I‘vaccine efficacy is maintained against Omicron after administration of a booster dose, especially against severe forms“confirmed Public Health France on January 26.

What is the situation in Denmark?

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:

– “SARS-CoV-2 variants of concern and variants under investigation in England”, British Health Agency, 25 February 2022

– “Coronavirus: circulation of SARS-CoV-2 variants”, updated on February 25, 2022, Public Health France

-“BA.2 is more transmissible than BA.1 but vaccinated people are less likely to become infected and to transmit the infection”, January 31, Statens Serum Institut.

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

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