There is continued interest in "L" vs "S" strains of #SARSCoV2 proposed in the manuscript academic.oup.com/nsr/advance-ar…. Please consider this thread to be a public peer review of this work. 1/8
This mutation appears to have happened very early on in the outbreak while the virus was still in Wuhan, China. Viruses with "L" and viruses with "S" have spread from Wuhan to the rest of the world. Visible at nextstrain.org/ncov?c=gt-ORF8…. 3/8 
Generally, the expectation among virologists is that a random single amino acid change will have little impact on virus behavior. My "null" model would be that this mutation just happened to occur on an early branch on the tree and any "impact" is due solely to epidemiology. 4/8
We had a similar story with Ebola virus in West Africa where a possibly impactful mutation occurred, but distinguishing between virological and epidemiological effects was hugely difficult. bedford.io/papers/bedford… 5/8
Any differences in apparent severity between these two genetic variants are most likely due to sampling of market-associated severe cases in Wuhan and missing the bulk of mild cases in this setting. 6/8
That said, we will continue to monitor spread of these two variants to look to see how frequencies behave over time and to look for possible differences in clinical outcomes, though at this point we don't see one variant outcompeting the other. 7/8
In summary, I don't think the strong conclusions of the manuscript are warranted. We will monitor these two genetic variants, but I see no reason to conclude they have important functional significance at this point. 8/8
