Is the new strain of SARS-CoV-2 more infectious than the last?

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A study published in Cell has revealed that a new variant of SARS-CoV-2, now the dominant strain circulating around the world, is more infectious in cell culture. Researchers from Los Alamos National Laboratory (NM, USA), Duke University (NC, USA) and the University of Sheffield (UK) collaborated on this study to analyze the D614G variant of the virus, which causes a small but effective alteration in the Spike protein.

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The D614G variant of COVID-19 quickly took over as the dominant strain soon after it first appeared earlier this year. “The D614G variant first came to our attention in early April, as we had observed a strikingly repetitive pattern,” explained Better Korber (Los Alamos), lead author of the study. “All over the world, even when local epidemics had many cases of the original form circulating, soon after the D614G variant was introduced into a region it became the prevalent form.”

Upon analyzing this novel highly recurrent pattern using geographic data from samples from the GISAID COVID-19 viral sequence database, the team discovered it to be the new dominant form at every geographic level.

SARS-CoV-2 generally has a low mutation rate compared with the viruses that cause influenza and HIV-AIDS, yet the D614G variant appears to have arisen as part of a group of four linked mutations.

Additional experiments reported in the study demonstrated that the D614G variant increases the virus’s infectivity in the laboratory.

“It’s remarkable to me, both that this increase in infectivity was detected by careful observation of sequence data alone, and that our experimental colleagues could confirm it with live virus in such a short time,” commented Will Fischer (Los Alamos), an author on the study.

“Data provided by our team in Sheffield suggested that the new strain was associated with higher viral loads in the upper respiratory tract of patients with Covid-19, meaning the virus’s ability to infect people could be increased,” Thushan de Silva (University of Sheffield) reported.

Fortunately, at this stage it doesn’t seem that this new strain causes more severe disease: “the clinical data in this paper from Sheffield showed that even though patients with the new G virus carried more copies of the virus than patients infected with D, there wasn’t a corresponding increase in the severity of illness,” explained Erica Ollmann Saphire (La Jolla Institute, CA, USA).

Korber noted: “these findings suggest that the newer form of the virus may be even more readily transmitted than the original form – whether or not that conclusion is ultimately confirmed, it highlights the value of what were already good ideas: to wear masks and to maintain social distancing.”

Moving forward, further in vivo study will be necessary in order to determine the full implications of this new dominant strain.

Sources: Korber B, Fischer WM, Gnanakaran S et al. Tracking changes in SARS-CoV-2 Spike: evidence that D614G increases infectivity of the COVID-19 virus. Cell doi:10.1016/j.cell.2020.06.043 (2020); www.lanl.gov/discover/news-release-archive/2020/July/0702-newer-variant-covid-dominates-infections.php; www.sheffield.ac.uk/news/nr/new-strain-covid-more-infectious-1.892276

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