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