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A coronavirus uses its spike protein to bind to ACE2 receptors on a human cell. Image: Shutterstock
What’s new about the mutated corona virus that you still don’t know
It is also in Switzerland now and is said to be much more contagious than its previous version – VOC-202012/01, as the mutant is now called, kept us busy at Christmas.
How often has the mutated variant of the Sars-CoV-2 virus appeared in Switzerland so far?
As early as December 24, the mutant was found in two patients who had arrived from Great Britain: one in the canton of Zurich, the other in the canton of Graubünden, the BAG announced. Since then, ETH has found the South African variant in two people who tested positive: one in the canton of Schwyz and the other in France. ETH has sequenced around 500 samples that tested positive. The English variant was not among them.
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What distinguishes mutated variants of the previously known Sars-CoV virus?
The mutant was first called VUI-202012/01 (virus under inspection), now it is called VOC-202012/01 (variant of interest). The mutation occurred in strain B.1.1.7. There were actually several mutations, including 17 so-called “non-synonymous” mutations. These are changes that have changed the order of amino acids in the RNA chain. This means that when copying the strand it reads differently and changes in the biology of the pathogen should be expected. There were 14 amino acid changes and 3 losses at any one time.
What do mutations mean for the biology of the pathogen?
The N501Y mutation deserves special attention. It affects the so-called spike protein S, with which the virus attaches itself to the host cell. The mutation changes the protein in the so-called RBD (Receptor binding domain), where the important biochemical processes with the ACE2 receptor take place. There one of the six amino acids was changed. It is believed that this mutation could make the virus more contagious. A related confirmation is still pending, it would have to be tested in the lab.
Why did the mutated virus come from England?
The COG-UK (Covid-19 Genomics UK Consortium) has sequenced more than 150,000 virus genomes and discovered the mutation. Other countries are not as active. Emma Hodcroft from the University of Bern told NZZ on Sunday that “about 100 samples per week” are sequenced in Switzerland. Apparently, the mutation originated in England. Fortunately, if not, they would probably have been discovered later.
If you don’t yet know the biology of the new virus, how can you tell that it is more contagious?
The statement is based on a mathematical model. Nicholas Davies from CMMID (Center for Mathematical Modeling of Infectious Diseases) and his team provided initial information on December 23 in a study that has yet to be reviewed. They were helped by the fact that 69-70del, a loss mutation of the new variant, leads to a negative result in some PCR tests when a virus chain is queried. However, the other two parts of the virus that were searched for in the samples worked. Using these partially negative results, it was possible to reconstruct the appearance of the mutant in south-east England. There the number of cases increased significantly.
There is talk of a 56 percent increase in infectivity. How bad would that be?
The best explanation for the increase in the number of cases is the assumption that the probability of infection (infectivity) caused by the virus has increased. According to Davies, it could be ruled out that the virus no longer reacts to antibodies (that would have been devastating due to the effect of the vaccine), that children and adolescents are infected more quickly and that the generational time is shortened (that infected people infect to others more quickly). Davies and his team calculated the increase in infectivity by 56 percent, which would mean that the R-value would increase by 0.4 to 0.5 points.
What else could you observe with the mutated virus?
The viral load of the samples was significantly higher. The smears contained greater amounts of viral material than before. Perhaps the virus multiplies faster in the throat. This was also demonstrated in PCR tests. Here, the relevant limit was reached earlier (after some breeding cycles).
What does increased infectivity mean for the later course of the pandemic?
It is good that the measures continue to work: reducing contacts, where possible, is still effective. Washing your hands and putting on a mask are still good advice. And obviously we don’t have to worry about the effectiveness of vaccines just yet. And if the mutated pathogen were to spread through the population and eventually became invisible to antibodies, the mRNA in the vaccine could be specifically reformulated. It remains to be seen if this would have greater consequences for production and approval. Of course, it is negative that the virus is spreading faster and more widely if useful measures are not taken. An R
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