IL2 and influenza: For instance, the herpes zoster vaccine stops the herpes virus from reactivating in the brain; the influenza vaccine lowers cerebrovascular events, a known risk factor for dementia (Raz et al., 2016; Tsivgoulis et al., 2018); and intravenous BCG instillation dramatically raises serum IL‐2 levels, which increases the quantity of neuroprotective Treg cells (Taniguchi et al., 1999).