The researchers behind the study say 20C-US has been spreading rapidly through the US since June, and predict it could soon become the dominant variant of Covid-19 in the US.

Recently, scientists at the University of Manitoba, in Winnipeg, Canada, also identified two emerging variants that have been spreading around the world and are associated with “high fatality rates” compared to the earlier virus. One features a mutation called V1176F in the spike protein, which occurs alongside another mutation called D614G.

The first letter in these mutation names indicates the amino acid that has been replaced, the number is its location on the protein, and the final letter is the new amino acid that has appeared at that site. The D614G mutation alone appeared relatively early on in the pandemic in Europe and caused a dramatic increase in how much virus was shed by patients it infected, helping it to spread more quickly. The addition of the V1176F mutation may alter this behaviour further, the Canadian researchers say, and it has appeared in several countries independently, suggesting it gives the virus an advantage.

The other variant they identified appeared rapidly in Australia and carries a S477N mutation, which seems to have increased the virus’s ability to bind to human cells.

The researchers warn that these two new mutations “may pose significant public health concerns in the future” if they continue to spread and provide the virus with an advantage. They add that Covid-19 appears to be “evolving non-randomly and human hosts shape emergent variants with positive fitness that can easily spread into the population”.

These signs of adaptation by the virus are not entirely surprising to scientists. In most viruses and disease-causing bacteria, the use of treatments and vaccines causes them to evolve ways of escaping them so they can continue to spread. Those that develop resistance to a treatment or can hide from the immune system will survive for longer to replicate and so spread their genetic material.

“I do not see a reason that this evolutionary selective process would differ in a pandemic such as Sars-CoV-2 [the Covid-19 virus], compared to a geographically contained epidemic,” says Carolyn Williamson, head of the division of virology at the University of Cape Town and one of the researchers who identified a rapidly spreading South African variant in December. “One could speculate that the virus being exposed to different selective pressures in different regions of the world, together with rapid spread, may see these more favourable properties emerge more quickly, but we really don’t know.”

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