Study of a Live Attenuated Chikungunya Vaccine in a Previously Epidemic Area

Inclusion Criteria: 1. Aged ≥21 to ≤50 years on the day of enrollment. 2. Able to provide informed consent. 3. Available and accessible for the duration of the trial. 4. Able and willing to comply with all requirements of the study. 5. For female subjects, willing to practice a reliable form of contraception as specified in the protocol until five months after the second and final vaccination in accordance with recommendations following MMR vaccination. 6. Medical history and physical examination findings are considered normal or not clinically significant in the opinion of the Investigator. 7. Laboratory values are considered normal or not clinically significant in the opinion of the Investigator. 8. History of previous measles vaccination, either in childhood or as an adult if more than three months before participation in this study. Exclusion Criteria: 1. Taking medication or other treatment for unresolved symptoms attributed to a previous chikungunya virus infection. 2. Prior receipt of any chikungunya or other alphavirus vaccine. 3. Recent infection, including suspected chikungunya (within 1 week prior to Screening Visit). 4. History of an allergic or anaphylactic reaction to any vaccine. 5. An allergic reaction other than allergic contact dermatitis to any component of either vaccine (i.e., neomycin, gelatin), or a current egg allergy. Volunteers with a childhood history of egg allergy who are able to tolerate egg in their diet now will not be excluded on this basis. 6. History of an immunosuppressive disorder (such as human immunodeficiency virus \[HIV\] infection, common variable immunodeficiency), chronic infection (such as chronic hepatitis B or C), autoimmune disease (such as rheumatoid arthritis, systemic lupus erythematosus \[SLE\], autoimmune thyroid disease) or any medical condition that, in the opinion of the Investigator, could lead to an atypical immune response to the vaccine. 7. History of moderate or severe non-traumatic arthritis or arthralgia within 3 months of the Screening Visit. 8. Recent (within 30 days), current or anticipated use of any immunosuppressive or immune modifying medication including corticosteroids (excluding nasal, ophthalmic, and other topical preparations). 9. Other vaccination or planned vaccination within 4 weeks of either study dose (seasonal influenza vaccine excepted). 10. Measles vaccination or booster within the last 3 months or planned during the clinical study. 11. Receipt or planned receipt of blood products including immunoglobulins within 120 days of the Screening Visit. 12. Pregnant or lactating or planning pregnancy during the trial. 13. Known alcohol or other substance abuse that in the opinion of the Investigator affects the ability or willingness of the participant to understand and comply with the study protocol. 14. Participation in another clinical study within the past 30 days in which the subject was exposed to an investigational product (pharmaceutical product or placebo or device) or planned concurrent participation in another clinical study during the study period. 15. Relevant history of any medical condition that, in the opinion of the Investigator, may interfere with the safety of the subject (volunteer) or aims of the study. 16. History of neoplastic disease (excluding successfully treated non-melanoma skin cancer or cervical intraepithelial neoplasia) within the past 5 years or a history of any hematological malignancy. 17. Behavioral or psychiatric disease or cognitive impairment that in the opinion of the Investigator affects the ability or willingness of the participant to understand and comply with the study protocol. 18. Non-consent to storage of blood specimens for future research. 19. Persons in direct relationship with the Sponsor or its contract service provider, the clinical research organization (CRO) or its subcontractors, the Investigator or study site staff. Direct relationship includes first degree relatives or dependents (children, spouse/partner, siblings or parents), as well as employees (site or Sponsor). Employees of the University of Puerto Rico not directly employed by the Clinical \& Translational Research Center will not be excluded. 20. Any condition that would, in the opinion of the site Investigator, place the subject at an unacceptable risk of injury or render the subject unable to meet the requirements of the protocol.