Trial of the Immunogenicity, Safety, and Tolerability of rF1V Vaccine With CpG 1018® Adjuvant Compared With rF1V Vaccine in Adults 18 to 55 Years of Age

Inclusion Criteria: * Adults aged 18 to 55 years * Healthy participants or participants with pre-existing medical conditions who are in a stable medical condition. Pre-existing stable medical condition means a subject who: has full capacity of daily activity and no major medication modification within 3 months prior to Day 1; has not undergone surgical or minimally-invasive intervention or had any hospitalization/emergency room visit for the specific medical condition. * Able to comply with the protocol schedule and procedures. * Able and willing to provide written informed consent * If female of child-bearing potential and heterosexually active, has practiced adequate contraception for 28 days prior to vaccination and has negative pregnancy tests just prior to vaccination and has agreed to continue adequate contraception until 28 days after last study injection. Adequate contraception is defined as a contraceptive method with a failure rate of \< 1% per year when used consistently and correctly and, when applicable, in accordance with the product label. Examples include the following: * Combined (estrogen and progestogen containing) hormonal contraception associated with inhibition of ovulation: oral, intravaginal, or transdermal * Progestin-only hormonal contraception associated with inhibition of ovulation: oral, injectable, or implantable * Intrauterine device (IUD) with or without hormonal release * Vasectomized partner, provided he is the subject's sole partner and that he has received a medical assessment of the surgical success * Credible self-reported history of heterosexual abstinence for at least 28 days prior to vaccine administration * Female partner Exclusion Criteria: * A history of plague disease or have previously received any plague vaccine. * Active tuberculosis or other systemic infectious process. * History of human immunodeficiency virus (HIV), hepatitis B (HBV) or hepatitis C (HCV) infection, or positive test for antibody to HIV, HBV, or HCV * History of autoimmune disorder * History of sensitivity to any component of study vaccines * Body mass index ≥ 30 kg/m2 * Has received the following prior to the injection: * 14 days: * COVID-19 vaccine * Any inactivated vaccine * 28 days: * Any live vaccine * Systemic corticosteroids (more than 3 consecutive days) or other immunomodulators or immunomodulators immune suppressive medication, with the exception of inhaled steroids * Any other investigational medicinal agent * 90 days: * Immunoglobulins or any blood products * Granulocyte or granulocyte-macrophage colony-stimulating factor * Antisense oligonucleotides * Drugs/investigational agents with very long half-lives (defined as ≥ 60 days) * At any time: DNA plasmids or other genetic therapy intended to integrate permanently into host cells * If female is pregnant (known before or established at the time of screening), breastfeeding, or planning a pregnancy * Is undergoing chemotherapy or expected to receive chemotherapy during the study period; has a diagnosis of cancer within the last 5 years other than squamous cell or basal cell carcinoma of the skin * History or current evidence of any condition, therapy, or laboratory abnormality that might confound the results of the study, interfere with the subject's participation for the full duration of the study, or is not in the best interest of the subject to participate, in the opinion of the treating investigator * Oral temperature \>100.0°F at the time of vaccine administration. * History of acute myocardial infarction (AMI) or documented coronary artery disease (CAD)