Intranasal Sendai viral vector vaccination is more immunogenic than intramuscular under pre-existing anti-vector antibodies

► We examined immunogenicity of Sendai virus (SeV) vector vaccine in macaques. ► We compared intranasal (IN) and intramuscular (IM) SeV immunization. ► Both IN and IM SeV administrations are equivalently immunogenic in naive animals. ► IN SeV vaccination is more immunogenic than IM in pre-SeV-infected animals. ► This study implies potential immunogenicity of IN SeV vaccination even in humans.