COVID-19(11) SARS-CoV-2(10) coronavirus(6) Viral(5) variants(4) S1 domain(3) Evolution(3) responsible(3) Mutation(3) claimed(3) Infection(3) furin cleavage site(3) NTD(3) S1 subunit(3) proline(3) junction(3) Vaccine(3) exhibited(3) COVID-19 pandemic(3) Antigen(3) selection pressure(3) S2 subunit(3) complex(3) cryo-EM structure(3) the S1 subunit(3) S protein(3) docked(3) ACE2 receptor(3) Wuhan(3) RNA virus(3)