According to a paper published in Cell today, a specific change in the SARS-CoV-2 coronavirus virus genome, previously associated with increased viral transmission and the spread of COVID-19, is more infectious in cell culture. The variant in question, D614G, makes a small but effective change in the virus's Spike protein, which the virus uses to enter human cells.
"The D614G variant first came to our attention in early April, as we had observed a strikingly repetitive pattern,” Bette Korber, lead author of the study, explained. “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."
Geographic information from samples from the GISAID COVID-19 viral sequence database enabled tracking of this highly recurrent pattern, a shift in the viral population from the original form to the D614G variant. This occurred at every geographic level: country, subcountry, county, and city. The SARS-CoV-2 virus has a low mutation rate overall. The D614G variant appears as part of a set of four linked mutations that appear to have arisen once and then moved together around the world as a consistent set of variations.
"It's remarkable to me," commented Will Fischer, an author on the study, "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."
Fortunately, "the clinical data in this paper from [University of] 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," said Erica Ollmann Saphire, another author on the paper.
"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," Korber added.
Image: The variant in question, D614G, makes a small but effective change in the virus's Spike protein, which the virus uses to enter human cells. Image courtesy of Los Alamos National Laboratory.