Omicron subtype BA.2: WHO assesses dangerousness

The subtype of the contagious omicron variant, which first appeared in Great Britain, has now also spread to Germany. But how dangerous is the BA.2 subtype?

The omicron subtype BA.2 was already responsible for the rapid increase in corona infections in Denmark. The subtype now also accounts for around 24 percent of new infections in random samples in Germany. A first study from South Africa now provides information about the danger of the sub-variant.

Study from South Africa: The course of the disease is so dangerous

The study compared the course of the disease in people who had tested positive for the previously widespread omicron subtypes BA.1 and the new subtypes BA.2. In the investigation period from the beginning of December 2021 to the end of January 2022, the proportion of detected infections with subvariant BA.2 rose from three to 80 percent.

According to the researchers, no difference was found in the registered cases in terms of the frequency of hospitalization or the severity of the course of the disease in hospitalized people. COVID-19  is therefore similar in both subtypes of the omicron variant and is therefore usually comparatively mild.

The World Health Organization (WHO) endorsed this assessment of BA.2 on February 22nd.

A Japanese study recently published as a preprint raised concerns to the contrary. The study analyzed the effects of BA.1 and BA.2 on hamsters. The animals infected with BA.2 showed more severe damage in the lungs and in the tissues of other organs than in the hamsters suffering from a disease caused by BA.1. However, the results of animal experiments can often only be transferred to humans to a limited extent.

Omicron subtype: BA.2 spread study from Denmark

First evaluations from Denmark previously showed how effective BA.2 is in relation to the spread: The infection risk of the subtype is at least twice as high in unvaccinated and vaccinated people as with the omicron subvariant BA.1. Unvaccinated people also transmit the virus more easily than vaccinated or boosted people.

BA.2 also has a high immune escape. The neutralizing antibodies have difficulty recognizing the subvariant and therefore cannot adequately prevent infection with BA.2.

A total of around 8,500 primary infections in Danish households were evaluated and the chains of infection traced. What mechanisms cause infections to rise again as BA.2 spreads?

Higher contagion rate: BA.2 evades the immune response

BA.2 shows mutations in the spike protein as a subvariant of omicron. The spike protein is the part of the virus that enables the pathogen to dock onto human cells. The new omicron subvariant can evade the immune system response due to various mutations in the spike protein.

As  part of a vaccination or infection, the immune system  produces antibodies against the spike protein, which sound the alarm on renewed contact and begin to fight the virus.

Due to the structural changes in this protein, omicron is less well recognized by the antibodies, which can lead to a higher infection rate in vaccinated and recovered people.

The subtype differs from the original omicron variant in about 18 mutations. These could ensure that those who have been boosted and those who have recovered become infected with SARS-CoV-2 even more quickly.

Since other mechanisms, such as the T cells of the immune system, take effect in addition to antibodies, the number of infections could increase, but severe courses can still be prevented with the help of vaccination. Overall, BA.2 also has a lower risk of severe courses than, for example, the delta variant of the  coronavirus .

Influence on the development of the pandemic so far unclear

How BA.2 will specifically influence the infection process in Germany has not yet been finally clarified. According to the latest findings, at least an increase in hospitalization is rather unlikely. According to the Robert Koch Institute, however, BA.2 could lead to the number of infections in Germany falling more slowly or rising again due to the faster transferability.

 

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