This non-significant elevation in cellular immune responses could not be explained by an increase in the levels of cytokines IFN-γ, IL-4, and IL-5, cytokines involved in the type 1 and type 2 helper T cell responses, suggesting a type 0 helper T cell response in CFS patients after vaccination. This evidence concerns the gene IL4 and myalgic encephalomeyelitis/chronic fatigue syndrome.