ISG15 and infection: An inflammatory/type I IFN driven response to infection — as indicated by the expression of genes such as MX1, ISG15, and IFIT1 — was observed across all cell types in the unvaccinated and infected animals on day 2 after SARS-CoV-2 challenge relative to both naive animals and animals vaccinated with 30 μg mRNA-1273 (Figure 2A).