Three dimensional (3D) classification of the cryo-EM data revealed the presence of multiple conformational states of SARS-CoV-2 S corresponding to distinct organization of the SB domains within the S1 apex.  Approximately half of the particle images selected correspond to trimers harboring  a single  SB domain  opened whereas  the remaining half was accounted for by closed trimers with the three  SB domains closed.  A recently determined SARS-CoV-2 S structure also detected trimers with a single SB domain  opened but none entirely closed.