Primary high-dose murine norovirus 1 infection fails to protect from secondary challenge with homologous virus.

Human noroviruses in the Caliciviridae family are the major cause of nonbacterial epidemic gastroenteritis worldwide. Primary human norovirus infection does not elicit lasting protective immunity, a fact that could greatly affect the efficacy of vaccination strategies. Little is known regarding the pathogenesis of human noroviruses or the immune responses that control them because there has previously been no small-animal model or cell culture system of infection. Using the only available small-animal model of norovirus infection, we found that primary high-dose murine norovirus 1 (MNV-1) infection fails to afford protection against a rechallenge with a homologous virus. Thus, MNV-1 represents a valuable model with which to dissect the pathophysiological basis for the lack of lasting protection against human norovirus infection. Interestingly, the magnitude of protection afforded by a primary MNV-1 infection inversely correlates with the inoculum dose. Future studies will elucidate the mechanisms by which noroviruses avoid the induction of protective immunity and the role played by the inoculum dose in this process, ultimately translating this knowledge into successful vaccination approaches.