A robust reporting system for measurement of SARS-CoV-2 spike fusion efficiency

Dear Editor,During the COVID-19 pandemic,several SARS-CoV-2 variants such as Alpha,Delta,and Omicron successively became dominant worldwide.The infection of SARS-CoV-2 is triggered by the binding of spike protein to the cell-surface receptor angiotensinconverting enzyme 2(ACE2),which then fuses with cell membrane or lysosomal membrane after endocytosis.1 Extensive cell fusion and syncytia formation are a signature feature of severe SARS-CoV-2 and may play an important role in COVID-19 pathogenesis.Research has shown that SARS-CoV-2 spikemediated cell fusion leads to the formation of abnormal and multinucleated cells in the lungs of patients.2 Accordingly,the fusion ability of SARS-CoV-2 spike protein may be a leading indicator of viral infectivity and disease severity in SARS-CoV-2 patients.