SARS-CoV-2 jumped from bats to humans 'without much change'

The study, published in the journal PLOS Biology, showed that since December 2019 and for the first 11 months of the SARS-CoV-2 pandemic, there has been very little "important" genetic change observed in the hundreds of thousands of sequenced virus genomes.

"This does not mean no changes have occurred, mutations of no evolutionary significance accumulate and 'surf' along the millions of transmission events, like they do in all viruses," said researcher Oscar MacLean from the University of Glasgow.

Some changes can have an effect; for example, the Spike replacement D614G which has been found to enhance transmissibility and certain other tweaks of virus biology scattered over its genome. On the whole, though, "neutral" evolutionary processes have dominated.

"This stasis can be attributed to the highly susceptible nature of the human population to this new pathogen, with limited pressure from population immunity, and lack of containment, leading to exponential growth making almost every virus a winner," MacLean added.

"What's been so surprising is just how transmissible SARS-CoV-2 has been from the outset. Usually viruses that jump to a new host species take some time to acquire adaptations to be as capable as SARS-CoV-2 at spreading, and most never make it past that stage, resulting in dead-end spillovers or localised outbreaks," said Sergei L. Kosakovsky Pond, of the Temple University in the US.

Studying the mutational processes of SARS-CoV-2 and related sarbecoviruses (the group of viruses SARS-CoV-2 belongs to from bats and pangolins), the authors found evidence of fairly significant change, but all before the emergence of SARS-CoV-2 in humans.

This means that the "generalist" nature of many coronaviruses and their apparent facility to jump between hosts, imbued SARS-CoV-2 with ready-made ability to infect humans and other mammals, but those properties most have probably evolved in bats prior to spillover to humans, the study indicated.

The study is a collaboration between researchers in the UK, US and Belgium.