3. Results
3.1 Influenza/SARS-CoV-2 Omicron Subunit Combined Vaccine Induced High Levels of IgG Antibody Titers
BALB/c mice were intramuscularly immunized with PBS, HA, SARS-CoV-2 Omicron BA.5 S or HA+SARS-CoV-2 Omicron BA.5 S adjuvanted with MF59, respectively, three times at two-week intervals. Serum samples were collected one week after each immunization for HA or SARS-CoV-2 Omicron BA.5 S-RBD-specific IgG detection. Based on mouse sera collected on day 21, one week after the first boost immunization, as shown in Figure 2A, a high level of HA-specific IgG was observed in mice immunized with HA with no significant difference between the HA and HA+SARS-CoV-2 Omicron BA.5 S immunized groups. The level of IgG was significantly increased on day 35, one week after the second boost immunization, in mice immunized with HA and HA+SARS-CoV-2 Omicron BA.5 S, respectively. Similarly, based on mouse sera collected on day 21, as shown in Figure 2B, a high level of SARS-CoV-2 Omicron BA.5 S-RBD-specific IgG was observed in mice immunized with SARS-CoV-2 Omicron BA.5 S with no significant difference between the SARS-CoV-2 Omicron BA.5 S and HA+SARS-CoV-2 Omicron BA.5 S immunized groups. The level of IgG was significantly increased on day 35 in mice immunized with SARS-CoV-2 Omicron BA.5 S and HA+SARS-CoV-2 Omicron BA.5 S, respectively. As shown in Figure 2C and 2D, mouse sera collected on day 35 showed good binding ability with coated HA and Omicron S-RBD proteins.