In vivo experiments with the related virus SARS-CoV have shown that pre-vaccination of mice by recombinant vaccinia virus (VV) that expressed N protein during subsequent challenge resulted in the active production of Th1/Th2 pro-inflammatory cytokines (IFN-γ, IL-2, IL-4, IL-5) in animals and the development of severe pneumonia [52]. Here, IL2 is linked to susceptibility to pneumonia measurement.