2.2 Patients and sample collection
Serum samples were collected from the subsequent cohorts: healthy individuals uninfected prior to the global COVID pandemic; convalescents of wild-type SARS-CoV-2 with qPCR-negative results 2-8 weeks post-diagnosis in 2020; recipients of two-dose inactivated vaccines (2-3 weeks post-second vaccination), three-dose inactivated vaccines (3-5 months post-third vaccination), and four-mixed-dose vaccines (three-dose inactivated plus one-dose of alternative vaccine types, 2-4 weeks post-fourth vaccination). These vaccinated participants had no history of SARS-CoV-2 infection, as confirmed by regular qPCR screening tests. Serum samples from both vaccinated and unvaccinated individuals infected with the Omicron BF.7 variant were obtained when the subjects were tested qPCR-negative 2-9 weeks and 3-5 weeks post-diagnosis, respectively. Sera from golden hamsters infected twice with GX_P2V served as positive controls.