Surface electrostatic shift on spike protein decreased antibody activities against SARS-CoV-2 Omicron variant

•Antibodies against S2 subunit showed higher activity than the antibodies against RBD.•Glycosylation-removing treatments weekly increased antibody activities.•For the original strain, epitopes distribute on electrically neutral areas, which are positively charged in the Omicron strain.•When pH was adjusted to 5.0, antibody titers against Omicron increased exponentially.