Fig. 4. Duration and long-term protection of humoral response induced by mRNA-RBD.
a Passive immunization and challenge schedule. The blue and red arrow indicates the time of vaccination and sera transfer, respectively. b, c Groups of BALB/c mice (n = 10) received 15 μg of mRNA-RBD or a placebo. Half of the mice per group were euthanized at 8 weeks (short term) post vaccination, and massive sera were collected for further passive immunization. The other mice of the group were bled as desired and eventually euthanized at 26 weeks (long term) post vaccination to collect massive sera for further passive immunization. All serum samples were detected for IgG (b) and neutralizing antibodies (c) titers. d–e hACE2 transgenic mice (n = 5) were administered 350 μl per mouse of pooled short- and long-term immune sera and one day later were challenged with 1 × 105 FFU of SARS-CoV-2 via the i.n. route. d The hACE2 mice weight change was recorded after challenge. e Virus titers in lung. mRNA-RBD-H indicates the high-dose vaccine (15 μg). Data are means ± SEM (standard error of the mean). Comparisons were performed by Student’s t-test (unpaired, two tailed). Placebo animals = black circles; animals for long-term study = blue triangles; animals for short-term study = red squares; dotted line = the limit of detection. Data are one representative result of two independent experiments. Source data are provided as a Source Data file.