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.