SARS-CoV-2 is a single-stranded, positive-sense RNA virus (a virus whose genetic information consists of a single strand of RNA encoding viral proteins) with a genome that encodes 4 major structural proteins.^[2]
These 4 proteins are all required to produce infectious virions capable of replication:

• Spike protein (S), which mediates viral binding to and entry into cells
• Nucleocapsid protein (N), which houses the genetic material (RNA)
• Envelope protein (E) and membrane protein (M), which are required for organization and assembly of infectious virions^[2]
  
  

Like all RNA viruses (such as influenza A virus strains, which cause seasonal flu), SARS-CoV-2 has a higher mutation rate than DNA viruses (such as papilloma viruses which can cause warts, other skin lesions, and/or cancers; and herpes viruses which can cause chicken pox, cold sores, and/or encephalitis), resulting in increased genetic diversity. This results in a range of viral genetic variant sub-populations (known as quasispecies) with different viral fitness profiles (i.e., the ability to adapt and replicate) and potential for infection and disease virulence.^[6],[7]

The D614G SARS-CoV-2 spike protein (S) variant is the most common viral variant observed in mutational analyses reported in the literature.^[6],[8]
Genomic analyses of SARS-CoV-2 isolates have identified thousands of viral variants, including those that have been associated with increased COVID-19-related mortality. However, the viral variant garnering the most attention from researchers is the D614G spike protein (S) variant. 

• D614G is the most common variant observed in mutational analyses reported in the literature.^[6],[8]
• The D614G mutation reportedly increases the infectivity of SARS-CoV-2.^[6]
• Isolates of SARS-CoV-2 encoding the D614G mutation have been demonstrated to predominate over time in multiple geographic locations, including the European Union, China, and the U.S., implying that this change enhances viral transmission.^[8],[9]
• D614G has also been correlated with increased viral loads in COVID-19 patients.^[9]
• In an analysis of over 46,000 SARS-CoV-2 assemblies from almost 100 countries across the globe, a total of 12,706 mutations were identified, the majority of which were C→U transitions.^[10] Over 36,000 of the assemblies in the data set (77.8%) analyzed carried the derived allele from the D614G mutation.^[10]