CD4 and infection: TBEV-specific CD4+ T cells generated by vaccination, however, appear to react to a narrower range of viral targets compared to those generated by infection (61, 62) and while the majority of CD4+ T cells generated by vaccination, like infection, are polyfunctional (61, 64), vaccination-elicited IFN-γ responses reach only about half those elicited by infection in terms of both magnitude and number of virus-derived peptides capable of eliciting IFN-γ responses ((61), Figure 1 B).