Inclusion Criteria:
1. Able and willing to provide informed consent (and assent, as applicable) voluntarily signed by participant (and guardian, as applicable). Must verbalize understanding of the reason for and the procedures needed for the study and be willing to stay in the study for its entire duration.
2. Male or nonpregnant female 12 years of age and older.
3. In stable health per the investigator, and no hospital admission or major surgical procedure in the last 30 days before investigational product administration.
4. Negative for CHIKV antibodies as determined by CHIK IgM/IgG rapid diagnostic test (RDT), except for the Safety Subset which may be enrolled regardless of serostatus.
5. Women who are either:
1. Not of CBP: premenarchal, surgically sterile (at least 6 weeks post bilateral tubal ligation, bilateral salpingectomy, bilateral oophorectomy, or hysterectomy); or postmenopausal (defined as a history of ≥12 consecutive months without menses prior to randomization in the absence of other pathologic or physiologic causes, following cessation of exogenous sex-hormonal treatment). or
2. Meeting all the below criteria:
* Negative urine pregnancy test at screening visit
* Negative urine pregnancy test immediately prior to dosing
* Using an acceptable form of contraception per local standards and agree to use this for at least 8 weeks after investigational product administration
Note: Contraception requirements do not apply for participants in exclusively same-sex relationships and these participants should have no plans to become pregnant by any other means for at least 8 weeks after investigational product administration.
Exclusion Criteria:
1. Currently pregnant or breastfeeding.
2. Participation or planned participation in an investigational clinical study within 30 days of Day 1 (investigational product administration) and for the duration of the study. Note: Participation in an observational trial/study or follow-up phase of a trial/study may be eligible; however, participation in any other study should be discussed with the MM prior to enrollment.
3. History of severe allergic reaction or anaphylaxis to any component of the investigational product.
4. Prior receipt of any CHIKV vaccine (or therapeutic) or participation in a prior interventional CHIKV trial/study.
5. Prior documented, laboratory confirmed CHIKV disease.
6. History of any known congenital or acquired immunodeficiency or immunosuppressive condition that could impact response to investigational product administration (eg, leukemia, lymphoma, malignancy, functional or anatomic asplenia, alcoholic cirrhosis). Notes: i) history of basal cell and squamous cell carcinoma of the skin or carcinoma in situ of the cervix considered cured is not exclusionary; ii) history of malignancy considered cured from over 5 years from the date of screening with minimal risk of reoccurrence or relapse is not exclusionary; iii) documented controlled HIV infection (most recent tests show undetectable viral load and a CD4 cell count over 350 at the time of investigational product administration) is not exclusionary.
7. Prior receipt or anticipated use of systemic immunomodulatory or immunosuppressive medications including hyperimmune products, monoclonal antibody therapies, systemic corticosteroids, and/or therapy with alkylating agents, antimetabolites, or radiation from 6 months prior to screening through Day 22 visit (21 days \[-3/+5\] after investigational product administration). Note: i) for systemic corticosteroid uses at a dose or equivalent dose of 20 mg of prednisone daily for 14 days or more within 90 days of screening through Day 22 visit is exclusionary, and ii) use of inhaled, intranasal, topical, or ocular steroids is not exclusionary.
8. Receipt or anticipated receipt of any vaccine from 30 days prior to Day 1 through Day 22 visit.
9. Unstable medical condition in the last 30 days prior to Day 1.
10. Acute illness with or without fever (oral temperatures ≥38.0 ºC \[100.4 °F\]) within 14 days prior to investigational product administration.
11. Medical or social condition (eg, substance abuse) that could have an impact on the participant's ability to be compliant with study procedures/visits, as determined by the investigator.
12. Plans to travel outside the study area or move away for more than 3 consecutive months and will not be available for follow up at the site.
13. Identified as an investigator or employee of an investigator or study center with direct involvement in the proposed study, or identified as an immediate family member (ie, parent, spouse) of the investigator or employee with direct involvement in the proposed study, or identified as an employee of Bavarian Nordic, their families, contractors, agents, business partners, or anyone with a financial interest in the outcome of the study.
14. Any other medical condition that, in the opinion of the investigator, could adversely impact the participant's participation or the conduct of the study.
