Phase 2 Open-label Study of Alum-adjuvanted Chikungunya Virus-like Particle Vaccine (PXVX0317)

Inclusion Criteria: * Age 18 to 65 years old (inclusive) * For women of childbearing potential, a negative pregnancy test at screening and on vaccination day, practicing highly effective contraception for at least 30 days prior to vaccination, and willing to use a highly effective method of contraception through study completion. * Able and willing to provide informed consent for study participation prior to screening procedures. * Free of obvious health problems as established by medical history and clinical examination at screening and enrollment. * Available to participate for the duration of the study (approximately 8 months). * For the cohort of prior alphavirus vaccine recipients, a documented history of prior alphavirus vaccination. Exclusion Criteria: * Acute disease or febrile illness at the time of screening or enrollment. * Clinically significant cardiac, respiratory, rheumatologic or other medical or psychiatric condition that, in the opinion of the Investigator, places the subject at increased risk or affects their ability to understand and comply with study procedures. * Abnormal screening lab test result that, in the opinion of the investigator, obscures interpretation of the safety data or suggests a clinically significant cardiac, respiratory, rheumatologic or other medical condition that places the subject at increased risk. * Pregnant, lactating or planning to become pregnant during the study period. * Laboratory evidence of infection with Hepatitis B, C or HIV. * History of naturally (non-laboratory) acquired chikungunya or other alphavirus infection or travel to a WHO-designated chikungunya-endemic region within 30 days prior to Day 1. * History of acute allergic reaction to any component of CHIKV VLP vaccine or Alhydrogel®. * Current (30 days prior to Day 1) or anticipated use of systemic immunomodulatory or immunosuppressive medications. * History of splenectomy, immunosuppressive condition, autoimmune disease, or immunodeficient condition. * Family history of congenital or hereditary immunodeficiency. * Suspected or known current alcohol abuse that, in the opinion of the Investigator, would interfere with the subject's ability to understand and comply with study procedures. * Current intravenous drug use. * Prior receipt of an investigational chikungunya vaccine. * Receipt or planned receipt of any licensed vaccine from 30 days prior to Day 1 through Day 29 study visit. * Participation in another clinical trial during the study period in which an investigational product is administered. * For the alphavirus naïve group, history of prior alphavirus vaccination is exclusionary.