Evaluating the Live-Attenuated Human Parainfluenza Virus Type 3 Vectored Vaccine Candidate Expressing Ebolavirus Zaire Glycoprotein as the Sole Envelope Glycoprotein

Inclusion Criteria: * Adult males and non-pregnant females between 18 and 50 years of age inclusive * General good health, without significant medical illness, physical examination findings, or significant laboratory abnormalities as determined by the investigator * Agree to storage of blood specimens for future research * Available for the duration of the trial * Able to demonstrate understanding of key study concepts, study rationale, and study participation requirements by scoring greater than or equal to 70% on a written comprehension assessment in less than or equal to 3 attempts. * Willingness to participate in the study as evidenced by signing the informed consent document * Female subjects of childbearing potential must agree to have used effective birth control methods beginning at least one month prior to vaccination, and continuing with 'per label/fully effective use' for the chosen method for the duration of the study, from amongst these: * pharmacologic/hormonal contraceptives, including oral, parenteral, subcutaneous, and transcutaneous delivery; * condoms with spermicide; * diaphragm with spermicide; * intrauterine device; * absolute abstinence from heterosexual intercourse as a matter of normal preferred lifestyle; * or must be surgically sterile, or must be age 50 AND have had no menses at all for at least one full year. * All females must provide samples for urine and serum pregnancy testing prior to enrollment (immediately prior to each vaccination), as well as a statement of menstrual history and a summary of all potentially reproductive sexual activity for the month prior to each vaccination, and at each study contact throughout the study, and report if they may be pregnant immediately. * Willingness to refrain from blood donation during the course of the study * Willingness to refrain from receiving other vaccines or investigational products during the first 4 months of the study after enrollment * Willingness to follow admission and isolation requirements for the indicated duration per protocol. Exclusion Criteria: * Pregnancy as determined by a positive human choriogonadotropin (ß-HCG) test or history of recent unprotected intercourse in a woman of reproductive capacity * Currently breastfeeding * Evidence of clinically significant neurological, cardiac, pulmonary, hepatic, rheumatological, autoimmune, or renal disease by history, physical examination, and/or laboratory studies * History of intranasal pathology or evidence of structural abnormalities of the sinuses or nasal cavity upon examination * Behavioral or cognitive impairment or psychiatric disease that, in the opinion of the investigator, affects the subject's ability to understand and cooperate with the study protocol * Positive urine drug toxicology test indicating narcotic use or history of dependency * Have medical, occupational, or family problems as a result of alcohol or illicit drug use during the past 12 months * Other condition that, in the opinion of the investigator, would jeopardize the safety or rights of a subject participating in the trial, or would render the subject unable to comply with the protocol. * History of anaphylaxis * Current diagnosis of asthma or reactive airway disease (within the past 2 years) * Current history of allergic rhinitis requiring the use of medication in the 2 weeks before enrollment or the first 56 days of the study * History of Bell's palsy * Positive enzyme-linked immunosorbent assay (ELISA) and confirmatory test (e.g., Western blot or HIV-1/HIV-2 differentiation assay) for human immunodeficiency virus-1 (HIV-1) * Positive ELISA and confirmatory test (e.g., polymerase chain reaction (PCR) for virus) for hepatitis C virus (HCV) * Positive hepatitis B virus surface antigen (HBsAg) by ELISA test * Known immunodeficiency syndrome or history suggestive of impaired immune function * Use of corticosteroids (excluding topical preparations) or immunosuppressive drugs within 30 days prior to vaccination * Receipt of a live vaccine within 4 weeks or a killed vaccine within 2 weeks prior to study vaccination * History of asplenia. * Body mass index (BMI) less than 18.5 or greater than 40 * Receipt of blood or blood-derived products (including immunoglobulin) within 6 months prior to study vaccination * Current tobacco user unwilling to refrain from smoking, snuffing, vaping, or chewing for the duration of the inpatient study (subjects may use nicotine patches if needed) * Travel to an Ebola-endemic region at the time when cases were present or planned travel to West or Central Africa during the study period * Receipt of another investigational vaccine or drug within 30 days prior to study vaccination * Previous receipt of an investigational Ebola or Marburg virus vaccine, a chimpanzee adenovirus, or human parainfluenza virus (HPIV)-vectored vaccine, or any other investigational vaccine likely to affect interpretation of the trial data * Current or past (in the last 4 weeks) user of intranasal medications (including steroids, decongestants, or hormonal medications), or planning to use them within 28 days of study vaccination * Live or have close contact with vulnerable individuals, including infants, the elderly, or immunocompromised individuals (those with HIV/AIDS, malignancy, or transplant patients) * History of Liver disease.