claim: the furin cleavage site of sars-cov-2 spike protein is a key determinant for transmission due to enhanced infection in airway cells.
evidence_1: using lentiviral pseudotypes and a cell- culture adapted sars-cov-2 virus with a s1/s2 deletion, we show that the polybasic insertion is selected for in lung cells and primary human airway epithelial cultures but selected against in vero e6, a cell line used for passaging sars-cov-2.", "the furin cleavage site of sars-cov-2 spike protein is a key determinant for transmission", "we find this selective advantage depends on expression of the cell surface protease, tmprss2, that allows virus entry independent of endosomes thus avoiding antiviral ifitm proteins.", 
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  "sars-cov-2 has a unique polybasic insertion at the s1/s2 cs, which we demonstrate can be cleaved by furin.")