A Phase 3b multicenter, randomized, controlled, double-blind clinical trial was designed to evaluate the Immunogenicity (non-inferiority), 28 days post-immunization, for each Dengue and Chikungunya serotypes, as well as the safety, 21 days post-immunization, of the co-administration of the live attenuated Dengue and Chikungunya vaccines compared to the separate administration in adults aged 18 to 59 years without prior exposure to either arbovirus.