Figure 3.

Humoral Immune Responses after SARS-CoV-2 mRNA Vaccination

BALB/c mice received a single i.m. immunization with 30 μg of SARS-CoV-2 or Luc mRNA-LNP vaccines.

(A and B) S protein-specific IgG levels were determined by endpoint dilution ELISA (A) and neutralizing antibody (Nab) levels were measured by a VSV-based pseudovirus neutralization assay (B) before immunization and 4 and 9 weeks post immunization.

(C) Nab levels were further confirmed by microneutralization assay using serum obtained 9 weeks post vaccination. n = 10 mice/group. Naive mice were age matched, non-immunized BALB/c mice. (A–C) Symbols represent individual animals. Horizontal lines represent the limit of detection. End-point dilution ELISA, FRNT₅₀, and IC₅₀ titers below the limit of detection are reported as half of the limit of detection. Data shown are mean plus SEM.

(D) HEK293T cells transfected to express mFcγR1 were infected with SARS-CoV-2 pseudovirus or ZIKV virus-like particles preincubated with serially diluted anti-SARS-CoV-2 sera obtained 9 weeks post immunization or anti-ZIKV sera, respectively. Serum samples were pooled from 5 mice belonging to the same experimental group. Infection level was measured by luciferase assays. Mean ± SEM of three independent experiments is presented. Statistical analysis: (A and B) two-way ANOVA and (C) one-way ANOVA with Tukey’s multiple comparison on log-transformed data. (D) SARS-CoV-2: there are no significant differences when analyzed by two-way ANOVA with Tukey’s multiple comparisons test; ZIKV: two-way ANOVA with Sidak’s multiple comparisons test. ^∗p < 0.05, ^∗∗p < 0.01, ^∗∗∗p < 0.001, ^∗∗∗∗p < 0.0001.

See also Figure S3.