Using high-throughput pseudovirus assay in conjunction with neutralizing antibodies, Wang et al. investigated 80 natural variants and 26 glycosylation-spike (S) mutants of SARS-CoV-2 in terms of infectivity and antigenicity. 1They identified several mutations that can critically affect the virus infectivity and reactivity to neutralizing antibodies (Fig. 1).This study provides abundant and comprehensive data that will help us better understand the impact of mutations in S protein, and may contribute to future design of potent vaccine candidate and monoclonal antibodies (mAbs).SARS-CoV-2, the causative agent of the widespread COVID-19 pandemic, has caused at least 17.2 million infections and 671,000 deaths worldwide by the end of July 2020 (https://coronavirus.jhu.edu/).Currently, there is an urgent need for specific antiviral therapy and vaccine against SARS-CoV-2.The S protein is the key element of SARS-CoV-2 that determines the viral infectivity and induces host protective immune response. 2However, the rapid global spread provides the virus with an opportunity for natural selection, and several naturally occurring mutations in S protein have been identified.Given the crucial role of S protein in virus infection/transmission and vaccine/mAbs development, the authors investigated the biological significance of natural variants with amino acid change(s) and mutants at the putative N-linked glycosylation sites in the S protein.Previously, the authors have established a sophisticated pseudovirus assay system and constructed a series of pseudoviruses of emerging and re-emerging viruses, including MERS-CoV, rabies virus, Ebola virus, Marburg virus, Lassa virus, Chikungunya virus, Nipah virus, Rift valley virus, and others. 3,4 In this study, 106 pseudotyped viruses of SARS-CoV-2 were constructed to infect a series of human and animal cell lines, and the result demonstrated that the D614G variants or combined variants such as D614G + V341I, D614G + K458R, D614G + I472V, D614G + D936Y, D614G + S939F, and D614G + S943T showed 4-to 100-fold increased infectivity compared to the reference Wuhan-1 strain (GenBank: MN908947).Indeed, increasing the frequency and global dominance of the D614G variant has been seen, and the increase may suggest a fitness advantage of this variant.Potential association of D614G with higher viral loads in COVID-19 patients has been observed, but the link between the variant and disease severity is yet to be clarified. 5Furthermore, the increased infectivity and possibly increased production in the cell culture system of certain variants observed in this study may suggest a potential for development of the inactivated vaccine seed strain in the future.