KRT18 and infection: ,32,33 As an additional indicator of vaccine-mediated protection, we next evaluated whether vaccination and boosting with the bivalent mRNA vaccine, or prior intranasal infection with XBB.1.5, could suppress cytokine and chemokine levels in the lungs at 4 dpi following challenge with XBB.1.5 in K18-hACE2 mice (Figure 4).