Figure. Prevalence of neutralizing antibody titers to chimpanzee adenoviruses. Percentages of negative samples are not shown. Left column: Cameroon, black bars; Côte d'Ivoire, white bars; Nigeria: gray bars. Middle column: Thailand, black bars; US controls, white bars; US zoo keepers or animal handlers, gray bars. VNAs, virus neutralizing antibodies. Coded human serum samples that had been collected for other studies were obtained under an institutional review board exemption.