Flavobacterium spp. infections remain a major aquaculture industry issue and can cause major losses to fish stocks and economic implications. For salmonid producers, a common threat within this genus is F. psychrophilum , the causative agent of bacterial coldwater disease (BCWD). Recent advancements in BCWD disease management have included a live-attenuated vaccine that provides cross-protection from an array of F. psychrophilum strains. Emerging family Flavobacteriaceae isolates have also been identified in global fish health diagnostic cases and include novel, virulent Flavobacterium spp., and Chryseobacterium species. The cross-protective ability of this live-attenuated F. psychrophilum vaccine against novel Flavobacteriaceae was evaluated in juvenile rainbow trout. Fish developed high F. psychrophilum -specific antibody titers 8 weeks post-vaccination, with the vaccinated fish showing a greater response than mock-vaccinates (P<0.001) as expected. Fish were then challenged with two Chryseobacterium spp. (S25 and T28), a Flavobacterium spp. (S21), a mixed combination of S21:S25:T28 strains , and a standard virulent F. psychrophilum CSF259-93 strain . With respect to vaccination, the 259-93 V group had a relative percent survival (RPS) of 94.44% compared to the control (259-93 C) fish (P<0.001) . Interestingly, vaccinated fish also had a high RPS (85.18%) following the mixed Flavobacteriaceae infection. Protection was not observed following challenge with the single novel Flavobacteriaceae strains. Analysis of whole-cell lysates of bacterial strains revealed differences in protein profiles (SDS-PAGE), but antigenic regions were observed in S25 and T28 when probed with post-challenge sera from surviving fish the mixed S21:S25:T28 and CSF259-93 groups in a western blot . Results indicate that the live-attenuated F. psychrophilum vaccine provides indirect protection against mixed infections with novel Flavobacteriaceae, but further work is needed to determine the synergistic virulence mechanisms for these emerging isolates.