Significance Infections are known to perturb intestinal microbiome composition, but the underlying mechanisms and the implications of specific commensal species for antiviral immunity remain largely unknown. Here, we found that infection of mice with a fast-spreading and persistent, but not slow-spreading acute, viral isolate induced profound microbial dysbiosis, including blooming of Akkermansia muciniphila , that was largely caused by CD8 T cells and/or CD8 T cell-induced anorexia. Notably, administration of A. muciniphila into infected mice attenuated selected aspects of CD8 T cell responses, supporting its immunosuppressive potential in this context. Our findings bring about a role for CD8 T cells in promoting anorexia and microbial shifts after infection, including the enrichment of a fasting-associated commensal that can attenuate CD8 T cell responses.