What is BA.2?
Like the variant BA.1, which has been dominant in Europe to date, BA.2 is a subtype of the omicron variant of Sars-CoV-2. Both subvariants were noticed shortly after the discovery of Omicron at the end of November 2021 and differ from each other in about 20 mutations. While BA.1 initially prevailed and seemed to displace the dominant Delta variant, BA.2 initially went unnoticed. While PCR tests detect both subtypes, they cannot readily distinguish them. Initially, only BA.1 was identifiable as an omicron in an adapted PCR test, BA.2 was not.
If you want to track the spread of this subvariant, more complex and longer-lasting analyzes are necessary because there is no mutation in their genome. In Denmark, where significantly more samples are being sequenced, staff at the Statens Serum Institut in Copenhagen noticed in January that BA.2 appears to be spreading rapidly. BA.2 has now replaced BA.1 as the dominant variant in Denmark, and the proportion is also increasing in other countries.
How does the omicron subtype BA.2 spread?
The Berlin virologist Christian Drosten compared the two subtypes on Tuesday in the NDR podcast “Coronavirus Update” with two cars. The BA.2 engine therefore has “a few more horsepower.” BA.2 could possibly spread even faster than type BA.1, which is currently still causing maximum values for case numbers and incidences. Based on a study from Denmark that has not yet been reviewed by external experts, Drosten assumes that BA.2 could possibly have, as he put it, a “fitness advantage” and thus increased transferability.
How severe is the progression of the disease?
The data situation is still very sparse, which is why many things cannot yet be said with certainty. In January, the Statens Serum Institute wrote that initial analyzes showed no differences in the number of hospital admissions required. The very early observations from Denmark “suggest that there doesn’t seem to be a big difference between BA.1 and BA.2 in the severity of the disease,” emphasizes Sandra Ciesek, Director of the Institute for Medical Virology at the Frankfurt University Hospital. The French epidemiologist Antoine Flahault, head of the Institute for Global Health at the University of Geneva, said a few days ago that, according to the current state of knowledge, infections with the subtype were not more severe.
What does the vaccination do?
Vaccination would still have an effect against BA.2, albeit somewhat reduced compared to previous variants, write the Danish researchers in their study published on a preprint server at the end of January. However, you have to differentiate between the probability of being infected yourself, the probability of passing on the virus, becoming ill or having a severe course of the disease. According to the study, your own risk of infection from BA.2 could be more than twice that of BA.1. The ability for so-called immune escape is possibly greater, so that a previous infection or a vaccination could protect less well against BA.2 than against other variants.
The risk of transmission is also greatly increased in infected unvaccinated people, the researchers write, but not in vaccinated and boosted people. The researchers write that the higher susceptibility and transmissibility of unvaccinated people will possibly lead to a further increase in transmissions in unvaccinated children, for example in schools and daycare centers.
How is the situation in Germany?
In Germany, the proportion of the subtype is according to the youngest Weekly report of the Robert Koch Institute “still very low”. In the second week of the year, BA.2’s share was 2.3 percent, compared to 1.4 percent the week before. More recent data is expected this week. “BA.2 will also prevail with us”, writes the immunologist Carsten Watzl on Twitter. That “could lengthen the omicron wave”. Drosten also assumes that the proportion of BA.2 in Germany will increase, but possibly more slowly than in other countries due to the infection protection measures in force.
What does BA.2 mean for the discussion about easing?
Health Minister Karl Lauterbach (SPD) recently said in the federal press conference that he expected the number of infections to peak in mid or late February. If there are then significantly fewer infections, anti-corona measures could be relaxed. But because of BA.2, it could possibly take a little longer. The Green health politician Janosch Dahmen considers easing to be unlikely in the next four weeks. “It is possible that the trend reversal could be delayed by several weeks,” Dahmen told the Funke newspapers. The BA.2 distribution is expected to push the peak of the current wave further back.
The virologist Drosten sees a time threshold and a “planning horizon” for the relaxation of the situation in the coming Easter holidays. The transmission networks are currently fed from school operations. “The Easter holidays will then put a stop to it at the latest.” The then warmer temperatures should also have a reducing effect on the incidences. It remains to be seen whether BA.2 will have “completely taken over the field” by then.
Baden-Württemberg’s Prime Minister Winfried Kretschmann recently made it clear that he did not believe that the restrictions would end before mid-April. He did not specifically refer to BA.2.