Antivector immunity may limit the immunogenicity of adenovirus vector vaccines. We tested sera from individuals immunized with adenovirus type 4 and 7 (Ad4 and Ad7, respectively) vaccine or naturally infected with Ad4 for their ability to neutralize a panel of E1-deleted human and chimpanzee adenoviruses (ChAd). Small statistically significant increases in titers to ChAd63, ChAd3, human Ad35, and human Ad5 were observed. Neutralizing antibodies elicited by Ad4 infection or immunization results in a small amount of adenovirus cross-reactivity.