Fig. 4: LyomRNA-Omicron booster immunization engendered significant immune protection.

a–d BALB/c mice (n = 10) were immunized with the inactivated vaccine (0.65 U per dose) at D0 and D21, and a booster shot with heterogeneous LyomRNA-Omicron (5 μg) or homogeneous inactivated vaccine (0.65 U) was given at D42. The titers of plasma neutralizing antibodies against wild-type (a), Delta (b), Omicron-BA.1 (c), and Omicron-BA.2 (d) pseudoviruses were detected pre-boost, or at 14 days post boosting (dpb) and 28 dpb. e Six-year-old monkeys that had received two doses of inactivated vaccines (6.5 U dose per animal, twice at a 3-week interval) were boosted 18 months later with 50 μg LyomRNA-Omicron. Blood samples were collected before or 7, 14, 21, and 28 days after boosting with LyomRNA-Omicron. Neutralizing antibodies against the wild-type viruses, Omicron variants BA.1 and BA.2 were tested by a VSV-pseudovirus-based system. Dotted lines represent the blood pseudovirus-neutralizing antibody titers of nonimmunized control monkeys. f, g K18-hACE2 transgenic mice were vaccinated at D0, D21, and D61 with LyomRNA-Omicron (5 μg dose), and were lethally challenged at D73 with Omicron-BA.1. Survival (f) and lung virus load on D7 post challenge (g) were recorded. a–d The groups were compared by a two-sided Mann–Whitney test. *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001. Data are presented as the geometric means ± 95% confidence interval (a–e) or means ± SEM (g).