Figure 8.

Passive serum transfer provides some but not complete protection against cross-variant challenge

129S1 mice were immunized with IM mRNA prime/boost, IN NE/IVT/S prime/boost, or with IM mRNA prime followed by IN boost with S alone or adjuvanted with NE/IVT at a 4-week interval. Vaccine doses consisted of 0.4μg of mRNA and 15 μg S protein. At 2 weeks post-boost, 150 μL of sera pooled from each treatment group was passively transferred to naive mice, which were subsequently IN challenged with 10⁴ pfu of B.1.351. Viral titers in the (A) lungs and (B) nasal turbinates were measured at 4 d.p.i. by plaque assay. (n = 4–5/group; ∗p < 0.05, ∗∗p < 0.01 by Mann-Whitney U test.