A new variant of the Sars-CoV-2 coronavirus is spreading in Great Britain – and at an alarmingly rapid pace. The strain B.1.1.7. According to initial findings, it could be more infectious than the previous variants of the coronavirus, because at least some of its mutations apparently facilitate the binding of the virus to our cells. At least there is no evidence to date that this is why the vaccines become ineffective or that this strain causes more severe disease. However, quite a bit of testing and research is still necessary in order to correctly assess the effects of this virus strain on the pandemic.
The Sars-CoV-2 coronavirus is actually one of the viruses that mutate slowly: On average, only one or two mutations develop per month that persist in the virus population and then form new branches in the genetic family tree of the coronavirus. Such already known variants of Sars-CoV-2 include the so-called G614 strain, a mutant that emerged in early spring and has now become the dominant form worldwide. In the summer of 2020, the 20A.EU1 strain was established in Spain, which was brought into other European countries by holidaymakers returning. Only a few weeks ago, mutated coronavirus variants also caused concern, which developed on Danish mink farms and were then transmitted back to humans. These
“Cluster 5” mutant died relatively quickly and now seems to have disappeared from the human population.
Unusually many mutations at once
Now there is news of another new variant of the coronavirus. This B.1.1.7. The virus strain baptized was first detected in samples from southern England and London on September 20 and 21, 2020. More than 1,600 cases in Great Britain can now be clearly assigned to this strain, but epidemiologists assume far more infections with B.1.1.7. out. According to Patrick Vallance, chief scientific advisor to the British government, this virus strain made up around 26 percent of the cases tested in mid-November. In the second week of December this proportion had already increased significantly. “In London, 60 percent of all cases belonged to this new virus variant,” said Vallance at a press conference on Sunday.
As a research team led by Andrew Rambaut from the University of Edinburgh has found, this new strain of Sars-CoV-2 is characterized by an unusual accumulation of mutations. Accordingly, it differs from the Sars-CoV-2 original type by 14 replaced amino acids and three completely omitted protein building blocks. “Such a collection of 14 line-specific amino acid changes is so far unprecedented in the global genetic inventory of the Covid-19 pandemic,” said the researchers. They suspect that this strain may have developed in an immunocompromised patient with chronic infection. In these patients, the coronavirus infection can drag on for months, and their viral load is usually high. If these patients are then treated with convalescent plasma containing antibodies, this can lead to the particularly fit and highly reproductive virus variants surviving in them – and being transmitted to others.
First indications of increased infectivity
So far it is only rudimentary known what effects the mutations of the new virus strain have on the behavior of the virus. However, some genetic changes are cause for concern. Among them is N501Y, an amino acid alteration right in the protein’s binding site. “Spike protein position 501 is one of the key contact points for the virus to bind to receptors,” explain Rambaut and his team. Since the body’s antibodies and other immune reactions as well as the vaccines attach to this protein, changes in this area of the virus are particularly sensitive. In addition, changing the binding site on the spike protein can help the coronavirus to penetrate cells more effectively. This can make the virus potentially more transmissible, but it can also make it easier to multiply and lead to severe courses.
Initial experimental data suggest that the N501Y mutation can increase the affinity of the virus for the ACE2 receptor, the virus’ main docking site in human cells. In experiments with mice and cell cultures, this mutation increased the infectivity of Sars-CoV-2, as the researchers report. The same could apply to N439K and Y453F, two further mutations at the virus’ binding site. Another mutation, P681H, lies in the groove that separates the two subunits of the spike protein. It is known that this so-called furin groove is configured to make it easier for the coronavirus to penetrate our airway cells. In addition, it also plays a role in the transferability of the virus, as Rambaut and his team report.
In fact, there are first indications that the virus strain B.1.1.7. spreads faster and easier than previous coronavirus variants. Initial tests by British researchers suggest that the growth rate of this virus strain is around 70 percent higher than that of the original type. In addition, the British NERVTAG panel of experts estimates that the strain has an r-value that is 0.39 to 0.93 higher. The r-value indicates how many other people an infected person infects on average. The aim of fighting a pandemic is to keep this value below 1, because only then will the number of new infections decrease. By nature, the coronavirus has an r-value of around 3.5. “Increasing the r-value by 0.4 or more is extremely bad news,” said Paul Hunter of the University of East Anglia. “Because that could mean that even tough lockdown measures are not enough to achieve the target value of r less than 1.”
Vaccination effect apparently not affected
After all, the mutations of the new virus strain do not seem to make the previously developed vaccines against Covid-19 obsolete: “At this point in time, there is no reason to assume that one of the mutations discussed here will impair the vaccine’s effectiveness,” said the Covid- 19 Genomics UK Consortium on Saturday with. So far, there is also no clear evidence that the new strain is more aggressive and affects the severity of the course of Covid-19. There are reports from South Africa that a virus variant with one of the mutations of B.1.1.7. should lead to more cases of illness in healthy young people. However, it is still disputed whether this is not just due to a general increase in the number of cases. In the UK, on the other hand, there is so far no evidence of a more severe course.
However, some tests and research are still necessary to determine more precisely what effects the new virus strain B.1.1.7. actually on the course of the pandemic, which has transferability and immunological defense reactions. “The confirmed knowledge about the variant in the United Kingdom is still very sketchy,” comments the virologist Jörg Timm from the University Hospital Düsseldorf. “There are still no laboratory tests in which the biological properties of the variant are examined more closely. This also includes the question of whether the variant can pose a problem for the immune response. “
Source: Virological, December 19, 2020; Report COG uk December 20, 2020; NERVOUS DAY Meeting December 18, 2020, Science News, Science Media Center