No, SARS-CoV-2 does not have a higher transmission capacity. None of the currently documented mutations in the coronavirus appear to increase its transmissibility in humans, according to a study published today in “Nature Communications.”
Researchers at the University of London (Great Britain) reached this conclusion after analyzing the virus genomes of more than 46,000 people with Covid-19 from 99 countries.
‘The number of SARS-CoV-2 genomes that are generated for scientific research is staggering. At the beginning of the pandemic we realized that we needed new approaches to analyze huge amounts of data in near real time to identify new mutations in the virus that could affect its transmission or the severity of symptoms, “he explains Lucy van Dorp.
“Fortunately, we found that none of these mutations are causing Covid-19 to spread more rapidly, but we must remain vigilant and continue to monitor new mutations, particularly as vaccines are released.”
Coronaviruses such as SARS-CoV-2 are a type of RNA virus, which can develop mutations in three different ways: by mistake, by copying errors during viral replication, through interactions with other viruses that infect the same cell (recombination or rearrangement), or it may be induced by host RNA modification systems that are part of the host’s immunity (eg, a person’s own immune system).
Most mutations are neutral, while others can be beneficial or detrimental to the virus. Both neutral and advantageous mutations may become more common as they are transmitted to descendant viruses.
In collaboration with the Université de la Réunion and the University of Oxford, they analyzed a global dataset of virus genomes of 46,723 people with Covid-19, collected until the end of July 2020.
Researchers have identified 12,706 mutations in SARS-CoV-2, the virus that causes Covid-19. Exists for 398 mutations strong evidence that they have occurred repeatedly and independently. Of those, the researchers focused on 185 mutations that have occurred at least three times independently during the course of the pandemic.
To test whether mutations increase virus transmission, the researchers modeled the evolutionary tree of the virus and analyzed whether a particular mutation was becoming increasingly common within a given branch of the evolutionary tree, that is, testing whether, after a mutation develops a virus first, the offspring of that virus outnumber the closely related SARS-CoV-2 viruses without that particular mutation.
However, they found that the most common mutations are neutral for the virus. This includes a mutation in the spike protein of the virus called D614G, which has been widely reported as a common mutation that can make the virus more transmittable. The new evidence finds that this mutation is, in fact, not associated with a significant increase in transmission.
Furthermore, the study has found that most of the common mutations appear to have been induced by the human immune system, rather than being the result of the virus adapting to its new human host. This situation is in contrast to another analysis by the same team of what happened when SARS-CoV-2 then jumped from humans to farm minks.
“When we analyzed the genomes of viruses from mink, we were surprised to see the same mutation appear over and over again in different mink farms, despite the fact that these same mutations had rarely been observed before in humans,” says the researcher.
It is to be expected that a virus will mutate and eventually drift into different lineages as it becomes more common in human populations, but this does not necessarily imply that lineages will emerge that are more transmissible or harmful.
“The virus appears to be well adapted for human-to-human transmission, and may have already reached its optimal fitness in the human host when it was identified as a new virus,” says van Dorp.
The researchers caution that the imminent introduction of vaccines is likely to put new selective pressures on the virus to escape recognition by the human immune system. This can lead to the emergence of vaccine escape mutants, but the researchers say they can be quickly identified, allowing vaccines to be updated in time if necessary.