2.3 Animal Vaccination and Sample Collection
Twenty BALB/c mice were randomly divided into four groups with five mice
in each group. Mice were intramuscularly immunized as follows. Group 1
was immunized with PBS. Group 2 was immunized with 5 µg HA formulated
with an equal volume of MF59. Group 3 was immunized with 5 µg SARS-CoV-2
Omicron BA.5 S formulated with an equal volume of MF59. Group 4 was
immunized with 5 µg HA plus 5 µg SARS-CoV-2 Omicron BA.5 S formulated
with an equal volume of MF59. As shown in Figure 1, all mice were
immunized three times at two-week intervals. Serum was isolated from the
collected blood one week after each immunization, heat-inactivated at
56°C for 30 min, and then divided and frozen at -20°C in the
refrigerator for further use.