SARS SARS-like viruses ’ cutting sites.Finding furin cutting site surprise : “ That aha moment uh-oh moment , ” Garry says.When bird influenza viruses acquire ability cut furin , viruses often become easily transmissible.The insertion also created places sugar molecules could fastened spike protein , creating shield protect virus immune system.The COVID-19 virus ’ spike protein also binds tightly protein human cells called ACE2 SARS ( SN : 3/10/20 ) .Tighter binding may allow SARS-CoV-2 easily infect cells.Together , features may account COVID-19 contagious ( SN : 3/13/20 ) . “ It ’ peculiar , two features , ” Andersen says. “ How explain came ? I ’ got honest.I skeptical [ natural ] .This could happened tissue culture ” lab , viruses may acquire mutations replicate many times lab dishes .