We first determined whether we could detect short-term immunity to homologous MNV challenge and whether proteins encoded by specific MNV ORFs could elicit effective immunity. VRPs expressing ORF1, ORF2 and ORF3 of MNV1.CW3 and ORF2 of the HuNV Lordsdale (genogroup GII.4) and Chiba (genogroup GI.4) were produced for vaccination experiments. Western blots of VRP-infected cell lysates revealed proteins of appropriate sizes [29, 40] and additionally showed that hyperimmune polyclonal rabbit antisera to MNV [28] cross-reacted at low levels with VLPs from Chiba virus and Lordsdale virus ( Figure S1A ).