Trial to Evaluate the Immunogenicity and Safety of the Co-administration of Live Attenuated Dengue and Chikungunya Vaccines Compared to Separate Administration in Adults Aged 18 to 59 Years.

This randomized, controlled, double blind trial aims at assessing the safety and immunogenicity profiles of the co-administered Live Attenuated Dengue and Chikungunya vaccines comparatively to the isolated administration, in the adult population aged 18 to 59 years without prior exposure to either arbovirus.

Inclusion Criteria: 1. Male or female adults aged 18 to 59 years at the time of vaccination. 2. Signed informed consent by the participant or their legal representatives. 3. Ability to understand, based on the investigator's assessment, and agree to comply with all study procedures, including blood collection. Exclusion Criteria: 1. Participation in another clinical trial within 28 days prior to screening or planned participation in another clinical study during the trial period. 2. Pre-existing unstable health condition. An unstable health condition is defined as a disease requiring a change in treatment or hospitalization due to disease worsening within 90 days prior to screening. 3. Vaccination within 14 days prior to screening with any inactivated vaccine or within 28 days prior to screening with any live attenuated vaccine, or planned vaccination with any vaccine up to 28 days after study vaccination. 4. Known hypersensitivity to any component of the vaccines. 5. Thrombocytopenia or bleeding disorders that contraindicate intramuscular vaccination or venipuncture for blood collection. 6. Receipt of immunoglobulins, blood, or blood products within 180 days prior to screening. 7. Altered immunocompetence (immunosuppression, immunodeficiency, or immunocompromise) primary or secondary due to: Clinical conditions (including but not limited to renal failure, liver failure with cirrhosis, heart failure class III or IV according to the New York Heart Association, HIV infection, and asplenia). 8. Use of systemic corticosteroids (oral, intravenous, or intramuscular) at a dose equivalent to ≥20 mg/day of prednisone for more than 14 days or a cumulative dose greater than 280 mg within the last 90 days prior to screening. Topical, inhaled, and intranasal corticosteroids are allowed. Intermittent use (a single dose within the last 30 days prior to screening) of intra-articular corticosteroids is also allowed. 9. Receipt of antineoplastic agents, immunosuppressants, immunomodulators, or radiotherapy within the last 180 days prior to screening. 10. Malignancy at the time of screening or a history of malignancy with \