Large-scale analysis of viral genomes shows that coronavirus does not become more infectious and deadly.
In a new study by scientists from University College London and Oxford University, published on bioRxiv, viral genomes were studied in more than 15,000 COVID-19 patients from 75 countries.
The main conclusion of the authors, who sought to find out whether any of the mutations can make the virus more infectious or deadly, is this: none of the mutations currently registered in the SARS-CoV-2 virus seem to increase its transmissibility.
Mutations in coronaviruses can occur for various reasons: due to copying errors during replication, due to interaction with other viruses that infect the same cell, or under the influence of a host RNA that modifies the virus as a result of an immune response. Most mutations are neutral; others may be beneficial or harmful to the virus. And if a harmful mutation reduces the chances of the virus surviving, then a neutral or beneficial mutation can become common, as the virus passes them on to their “descendants”.
The authors of the new study, having studied the global database, revealed 6,822 mutations in SARS-CoV-2.273 mutations, as it turned out, occurred repeatedly and independently of each other. Of these, scientists chose 31 more mutations for a more detailed study, which occurred during the pandemic at least 10 times independently of each other.
To check whether mutations increase the transmission of the virus carrying them, the researchers modeled the evolutionary tree of the virus and found out whether a particular mutation is more common in a particular branch of the evolutionary tree — that is, whether the “descendants” of this virus are superior to their “close relatives” who have this mutation no. However, no evidence was found that any of the common mutations increase the transmissibility of the virus. It turned out that some common mutations are neutral, and most are even slightly harmful to the virus.
Among the mutations analyzed was a mutation in a viral spike protein called D614G - it was previously assumed that it could make the virus more transmissible. New data showed that this mutation is not associated with increased transmission of the virus.
Most common mutations, the researchers found, appear to be caused by the influence of the human immune system, and not by the adaptation of the virus to its new human host.
As the authors of the work summarize, one can expect that in the process of mutations, the virus will spread in different lines, spreading more and more among people. But this does not mean that any of the new lines will be more transmitted or dangerous.