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SARS-CoV-2 mutations do not appear to increase transmissibility

None of the mutations currently documented in the SARS-CoV-2 virus appear to increase its transmissibility in humans, according to a study led by University College London (UCL) researchers.

The research analysed a global dataset of virus genomes from 46,723 people with COVID-19, collected up until the end of July 2020, and identified 12,706 mutations, of which 398 occurred repeatedly and independently. Of those, the researchers focused on 185 mutations that occurred at least three times independently during the course of the pandemic.

There was no evidence that any of the common mutations increased the virus's transmissibility. Most of the common mutations were neutral for the virus, including the D614G mutation in the spike protein, which was suspected of increasing transmissibility.

Most of the common mutations appeared to have been induced by the human immune system rather than the virus adapting to its novel human host. This is in contrast with SARS-CoV-2 jumping from humans into farmed minks.

Lead author, Professor Francois Balloux from UCL Genetics Institute, explained: "We may well have missed this period of early adaptation of the virus in humans. We previously estimated SARS-CoV-2 jumped into humans in October or November 2019, but the first genomes we have date to the very end of December. By that time, viral mutations crucial for the transmissibility in humans may have emerged and become fixed, precluding us from studying them."

The researchers caution that the introduction of vaccines is likely to exert new pressures on the virus to escape recognition by the immune system, potentially leading to the emergence of vaccine-escape mutants.

Professor Balloux concluded: "The news on the vaccine front looks great. The virus may well acquire vaccine-escape mutations in the future, but we're confident we'll be able to flag them up promptly, which would allow updating the vaccines in time if required."


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