A spike protein mutation D614G became dominant in SARS-CoV-2 during the COVID-19 pandemic1,2. However, the impact on viral spread and vaccine efficacy remains to be defined. Here, we engineer the D614G mutation in the USA-WA1/2020 strain and characterize its effect. D614G enhances replication on human lung epithelial cells and primary human airway tissues through an improved infectivity of virions. Hamsters infected with the G614 variant produced higher infectious titers in the nasal washes and trachea, but not lungs, confirming clinical evidence that the D614G mutation enhances viral loads in the upper respiratory tract of COVID-19 patients and may increases transmission. Sera from D614-infected hamsters exhibit modestly higher neutralization titers against G614 virus than against D614 virus, indicating that (i) the mutation may not reduce the ability of vaccines in clinical trials to protect against COVID-19 and (ii) therapeutic antibodies should be tested against the circulating G614 virus. Together with clinical findings, our work underscores the importance of this mutation in viral spread, vaccine efficacy, and antibody therapy.
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