Even though the mechanism underlying the occurrence of post-vaccination headache is currently unknown, this symptom could be a consequence of a homoeostasis disorder deriving from humoral and cellular immunity induced by the vaccine, which are characterized by an increase in inflammatory cytokines (i.e., interferon gamma, interleukin-6, CXC ligand 10) leading to a plethora of symptoms that also include headache [16,17]. Here, IFNG is linked to Headache.