Animal immunization and challenge studies

Animal immunization and challenge studies. BALB/c mice were immunized with SARS-CoV-2 RBD-Fc protein. Briefly, female mice (6 to 8-week-old) were randomly divided into two groups, and subcutaneously (s.c.) vaccinated with RBD-Fc (10 μg /mouse) or PBS control in the presence of aluminum (100 μg/mouse) adjuvant and boosted with the same immunogen and adjuvant at 2 weeks. Sera were collected 2 weeks after primary and boost immunization to detect SARS-CoV-2 S specific antibodies and neutralizing antibodies as described below. Four weeks after the boosted immunization, mice were inoculated intranasally with MASCp6 (1.6×10⁴ PFU/mouse). All mice were observed daily. On day 5 post-infection, five mice in each group were sacrificed, and their lung tissues were subjected to viral RNA loads analysis and lung pathological analysis.