Is the D614G coronavirus mutation more contagious than the original strain?

d614g mutation
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An altered version of the coronavirus called the D614G mutation now accounts for close to 85% of all COVID-19 cases in the world. Experts believe new research suggests the mutation is more contagious than the original COVID-19 strain. 

A recent study published in the peer-reviewed medical journal mBIO surveyed more than 5,000 coronavirus patients at Houston Methodist hospital and found that 99.9% of infections were caused by the D614G form of the coronavirus. 

D614G is a mutation from the earliest strain of the coronavirus, a variant now called the “D Strain.” D614G was first spotted in China and Germany in late January before spreading through Europe and the United States in February. 

The coronavirus or SARS-CoV-2 encodes its genomes in RNA. Other viruses that do so, such as HIV and influenza, tend to mutate quickly and often because enzymes regularly make errors when copying RNA. So far, the SARS-CoV-2 rate of change is only two single-letter mutations per month, half the rate of influenza and one quarter that of HIV, according to Emma Hodcroft, a molecular epidemiologist at the University of Basel in Switzerland.

Even so, there have been more than 12,000 mutations in SARS-CoV-2 genomes. Many mutations do not alter the shape of the protein, but the D614G mutation did so. The mutation occurs at the 614th amino-acid position of the spike protein. The change is small and simple. One amino acid is changed from a D (aspartate) to a G (glycine). 

In March, D614G made up a quarter of COVID-19 cases before spiking to 70% of cases in May. A September study found 99% of cases in a New York hospital were of the G Strain. The recent Houston study mirrored the findings, leading experts to deem D614G as the ubiquitous strain of COVID-19 spreading throughout the world. 

Several studies have suggested that the D614G mutation is more contagious than the original strain. In August, Paul Tambyah, president-elect of the International Society of Infectious Diseases, said D614G was more infectious but less deadly. Experts within the medical community pushed back against the comments, calling them premature and speculative, but further evidence from October is beginning to prove otherwise. 

The University of Texas published a study in late October that compared the D and G strains. It found D614G to be more infectious as it “enhanced SARS-CoV-2 replication in the upper respiratory tract through increased virion infectivity,” the authors wrote. 

One of the major concerns with virus mutations is the way they can impact vaccine development. Scientists were relieved by a recent study from the Commonwealth Scientific and Industrial Research that found the D614G will not have an impact on the effectiveness of current vaccines in development. 

“Despite this D614G mutation to the spike protein, we confirmed through experiments and modeling that vaccine candidates are still effective,” said Professor Seshadri Vasan from CSIRO, who led the study. “We’ve also found the G-strain is unlikely to require frequent ‘vaccine matching’ where new vaccines need to be developed seasonally to combat the virus strains in circulation, as is the case with influenza.” 

In mid-November, both Pfizer and Moderna announced that early data showed their vaccine candidates were at least 94% effective.

Sources: Daily Mail, Nature.com, mBIO, Reuters

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