Our pilot immunogenicity studies with the BioNTech COVID-19 mRNA vaccine in mice showed that doses of 2.5, 5.0, and 10 μg mRNA elicited comparable frequencies of antigen-specific CD8 T cells in the spleen, but responses to the 10 μg dose showed low variability (Supplemental Figure 1; supplemental material available online with this article; https://doi.org/10.1172/jci.insight.172510DS1). Here, CD8A is linked to COVID-19.