Could a mutation be behind the coronavirus' fast spread through Europe and the US?
Researchers in the US think the particular strain of the SARS-CoV-2 virus behind the COVID-19 pandemic ravaging the West might be more contagious than others, explaining why many of the world's wealthiest countries have had such terrible outbreaks.
The World Health Organization in early March declared Europe the epicentre of the pandemic, despite the virus first being detected in faraway China. By the end of the month, the US was the new frontrunner - particularly New York.
Genetic analysis later showed most of the US strains of the disease came from Europe, not China. The US has the highest confirmed COVID-19 death toll in the world, followed by the UK, Italy, Spain and France.
In a new paper published online, researchers at the Los Alamos National Laboratory in New Mexico say after analysing 6000 different SARS-CoV-2 genetic sequences from around the world, they've found a mutation in a dominant strain which could explain what's going on.
"The story is worrying, as we see a mutated form of the virus very rapidly emerging, and over the month of March becoming the dominant pandemic form," study leader Bette Korber wrote on her Facebook page.
"When viruses with this mutation enter a population, they rapidly begin to take over the local epidemic, thus they are more transmissible."
The mutation is on the virus' spike protein, which it uses to infect healthy cells. Much of the research into possible vaccines for the disease has focused on the spike protein, but if they're designed to protect against an older form of the protein that's been displaced, they might not be as effective.
The paper - published as an "early warning" - has not been peer-reviewed, and was met with scepticism from some experts.
"They found a mutation that became dominant over time but didn't do anything to show its functional significance in transmission," Columbia University virologist Angela Rasmussen tweeted. She said a similar mutation was seen in the Ebola virus, but when tested experimentally, it did nothing to increase its infectiousness.
"[The mutation] may well have functional importance. It may even increase transmissibility. But we won't know until this is tested experimentally... While it's good to know that this mutation appears to be under positive evolutionary selection, and we should study it to see if it is important for viral fitness or infectivity, it's way too premature to be sounding an 'early warning' alarm."
Others have suggested it might not make the more virus more contagious - it could just be that that version of the virus happened to be the one that made landfall in Europe and the US first; or that it just happened to be the first to infect countries which failed to lock down early - the US, UK, Italy and Spain among those - giving it a better chance to spread.
But genetic analysis showed the new strain of the virus, even if introduced to a population after a version closer to the original version first detected in Wuhan, appears to quickly take over. The paper says this indicates it has a "fitness advantage relative to the original Wuhan strain that enables more rapid spread", even if it's not clear why.
The good news is it doesn't appear to make the resulting disease any worse than it already is.
Much of the research into the virus and COVID-19 has been published online prior to peer-review, in an effort to share knowledge quickly in the urgent hunt for a vaccine. The paper itself notes its findings should not be reported as "established information".