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Overall, the genetic sequence diversity of SARS-CoV-2 is low. However, because most vaccine and antibody therapies target the trimeric spike protein, any alterations in its genetic sequence could have important implications.
Now, researchers in the U.S. and U.K. have queried the Global Initiative for Sharing All Influenza Data (GISAID) SARS-CoV-2 sequence database looking for changes in the spike protein genetic sequence of more than 0.3% from the Wuhan reference. Using this criterion, they identified a D614G amino acid change caused by a point mutation.
Examination of viral strains from Europe, North America, Australia, and Asia showed that the G614 variant increased in frequency over a several month period, even when D614 was initially dominant. In time-series analyses, 30 of 31 regions showed an increase in frequency of G614 over D614. Examination of viral sequences from 999 patients hospitalized with COVID-19 showed that the cycle threshold was lower, indicating a higher viral load with the G614 variant than with the D614 virus. Higher viral titers were seen in pseudovirus with the G614 variant than with the D614 variant. However, hospital outcomes were similar with either variant, and convalescent sera from 6 patients demonstrated equivalent or better neutralizing ability against G614 than against D614.
Korber B et al. Tracking changes in SARS-CoV-2 spike: Evidence that D614G increases infectivity of the COVID-19 virus. Cell 2020 Jul 3; [e-pub]. (https://doi.org/10.1016/j.cell.2020.06.043)
Comment
Although SARS-CoV-2 is not highly mutable, these data demonstrate that variants may arise quickly and have profound effects on the COVID-19 pandemic. Even though this variant appears to be more infectious, it did not appear to be more virulent, and, in limited assays, it was still inactivated by convalescent sera. However, continued surveillance and vigilance are required because we may not be as fortunate with the next variant.