Each of the targeted inner-cavity site at the S2 subunit of the monomeric spike of SARS-CoV-2, including their Omicron variants, contained part of the HR1 heptad-repeat (910 to 988) and CH central helix (986-1033) extending from the 960 to the 1010 amino acid residues, apparently accessible only when in the prefusion all-down state, each of the S2 trimeric α-helices are bended in an spring-loaded mechanism. The α-helix bending unfolds during the early steps of fusion elongating to one trimeric coiled-coil bundle of rigid linear α-helix conformations at the postfusion states. Similar spring-loaded switch mechanisms but with other amino acid α-helix sequences have been demonstrated in many other enveloped viruses .