Do SARS-CoV-2 mutations make the virus more infectious? Fears are not yet substantiated
As the virus multiplies, mutations are generated constantly. In the case of SARS-CoV-2, viral RNA copying errors play a major role in this. But they rarely happen. The fact is that SARS-CoV-2 has a “special” RNA-dependent RNA polymerase capable of correcting mistakes made by it. Some, but not all! There are other mechanisms of mutation (genetic recombination, cellular systems of “RNA editing”). But, regardless of how the mutation originated, it is essentially a change in the sequence of nucleotides in genomic RNA.
46,723 SARS-CoV-2 genomes from 99 countries were analyzed (the length of each sequence is 29903 nucleotides). Differences from the genomic sequence of the Wuhan isolate were identified at 12706 genomic positions. Accordingly, 17197 genomic positions were constant. This does not mean that mutations at these genomic positions do not occur at all. It’s just that these mutations reduce the viability of the virus so much that its offspring are “out of the game”. With a random selection of pairs of isolates from this dataset, the average number of differences between them was about 8.
On the one hand, this means that there are almost no 100% identical SARS-CoV-2 isolates. But on the other hand, compared to other viruses, the degree of genetic diversity is low and there is reason to believe that the evolution of SARS-CoV-2 is rather slow and dramatic changes in its biological characteristics are unlikely.
I come to the main and most difficult thing – the assessment of the “infectiousness” (contagiousness / transmissibility) of various SARS-CoV-2 mutants. It is logical to assume that if the same mutations arose independently (in completely different branches of the tree) two or more times, then they have selective advantages. In evolutionary theory, these mutations are called “homoplasies.” If among the genetic variants of SARS-CoV-2 there are those that are more infectious, it is most likely to find them among the homoplastic mutations. About 400 of them were identified in this work. But ho
This is not a trivial task, but it was solved. The details are too complex for a layman. The bottom line is to calculate more often or not homoplastic mutants give “daughter shoots” in the phylogenetic tree. It turned out not. None of the SARS-CoV-2 mutants showed any indication that their transmissibility was increased. This conclusion is valid for the data accumulated by September 2020.wе can the degree of infectivity be assessed using phylogenetic analysis tools?Поділитися цим: