Covid-19

Experts urge caution on reports of new virus strain

Reports of a new, more transmissible strain of the coronavirus may not be all they're cracked up to be, Marc Daalder reports

Media reports of a more infectious strain of SARS-CoV-2, the virus that causes the Covid-19 disease, may have jumped the gun, experts say.

"There is no evidence yet that this D614G virus is more contagious or causes a more severe infection in humans," Jemma Geoghegan, a senior lecturer in viral evolution with a focus on infectious diseases at the University of Otago, told Newsroom.

Some of the reports were sparked by an early academic paper that was criticised by other scientists. The paper noted that virus variants with a particular mutation, where the 614th amino changed from a D (aspartate) to a G (glycine), were more common in Europe and also noted that the coronavirus appeared to be transmitting more quickly there.

Viruses mutate frequently and the new coronavirus is thought to mutate about 23.92 times a year, or twice every month on average. The vast majority of these mutations have no impact whatsoever on the virus' transmissibility or severity.

"We have always expected that the virus would mutate as it adapts to its new human host.  The original isolate was perhaps surprisingly good at being transmitted, and very successful, which removed some of the selection pressure for new mutations," the Prime Minister's Chief Science Advisor, Juliet Gerrard, told Newsroom.

When the early paper emerged, Geoghegan says, it was criticised as mistaking correlation for causation. There were plenty of reasons the virus could have transmitted more in Europe, including laxer public health measures or a colder climate.

This map from Nextstrain shows the prevalence of the D614G mutation in genomes sequenced around the world. The more yellow in each country's pie chart, the more common D614G is.

"There's so many reasons why a mutation would increase in frequency just by chance," Geoghegan said.

It is also rather common in New Zealand. About two thirds of our cases are likely to have had the D614G mutation, Gerrard said on Twitter. Geoghegan told Newsroom about half of New Zealand's clusters had the mutation, but there was little difference observed in the rate of spread between them.

"The D614G mutation is certainly very widespread but it is very hard to ascertain with any certainty whether it is more transmissible, and there doesn’t seem to be any solid evidence yet that there is a difference in clinical outcomes," Gerrard said.

What most intrigued Gerrard was that the mutation occurred in the spike protein on the virus, which is a target of considerable vaccine research.

"Some vaccine strategies are dependent on recognition of the spike protein, and so researchers in this arena will be especially mindful to ensure that any vaccine candidates are robust to this (and other) mutations in this important protein," she said.

Then, a few days ago, a new study was published which found that the D416G mutation infected cells more quickly in cell cultures in a controlled lab environment. This has led to a second round of concerns about the strain, with Asian media outlets in particular raising worries that countries like China or Thailand could be vulnerable to the European mutation.

Geoghegan says this too is jumping the gun.

"It's hard to draw conclusions from cell cultures to relate it to what's actually happening in humans. It doesn't always correlate," she said.

"That's why I'm very hesitant to say it means anything. Now we need to do a lot more research to try and understand how it changes in humans."

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