A prophylactic or therapeutic vaccine for use in protecting mammals such as humans or animals against Venezelan Equine Encephalitis virus (VEE) is described. In particular, the vaccine comprises a recombinant virus such as a recombinant vaccinia virus which is able to express the structural genes of VEE in attenuated form, which has been modified to increase the protective effect of the vaccine. This is achieved by modifying the sequence of the attenuated VEE strain and/or putting this under the control of modified promoter which increases expression from the vector. Formulations of the vaccine as well as methods of treatment using the vaccine are also described.