IFNG and bacterial infectious disease: Geohelminth exposures may suppress vaccine immune responses through three possible immunological mechanisms (Figure 2): 1) Th2 polarization-with a switch in Th1 towards Th2 responsiveness causing reduced Th1 responses (i.e. IFN-γ) responses important for antiviral immunity and immunity against bacterial infections (e.g. Mycobacteria [78]and Bordetella pertussis [79]).