Immune interference in the setting of same-day administration of two similar inactivated alphavirus vaccines: Eastern equine and western equine encephalitis

► We see immune interference with same-day administration of two similar inactivated vaccines. ► ACIP dogma regarding same-day administration of inactivated vaccines is disproven. ► Gender differences were seen in vaccine response rates. ► Immunological mechanisms of induction of inactivated viral vaccine protection need further study.