Since older adults may be more susceptible than younger adults to norovirus infection or disease [5] , we determined whether increased age altered vaccine efficacy. Prior work has shown that mice older than 1 year of age have diminished vaccine responses to SARS virus antigens [42] . We therefore compared vaccine efficacy in adult (8 week old) and aged (14 month old) mice. Adult and aged mice were vaccinated and challenged as before. In contrast to studies using SARS virus antigens [42] , aged mice responded as well as adult mice to MNV ORF2 vaccination in both the distal ileum and MLN ( Figure 1D and 1E). Despite this protective effect, sera from vaccinated aged mice had significantly lower anti-MNV ORF2 IgG compared to adult mice ( Figure S1C ). These data indicated that protection against MNV infection occurred in the absence of robust serologic responses, again raising the possibility that T cells play a fundamentally important role in vaccination against MNV.