The purpose of this study is to compare the immune responses of two different doses (1.0 mg and 2.0 mg) and two different dosing schedules (two doses or three doses) of a mixed Hantaan virus (HTNV) and Puumala virus (PUUV) DNA vaccine in healthy participants. To maintain a blind, participants in the two-dose group will receive one dose of normal saline placebo. All of the groups will also receive a booster dose 6 months after first vaccination. The results will help to determine which dose and vaccination schedule will be best to move forward in the vaccine development process.

The study will enroll 4 randomized groups of 30 subjects each for a total of 120 subjects. These groups will be split so that 60 individuals receive the 1.0 mg dose and the other 60 receive the 2.0 mg dose. Every subject will receive a total of 3 injections on Days 0, 28, and 56. Half of each of these groups (n = 30) will receive 2 vaccine injections at Days 0 and 56 (normal saline placebo on Day 28) while the other half will receive 3 vaccine injections at Days 0, 28, and 56. All subjects will receive a booster dose at Day 168 to help assess immunogenicity with this booster dose. All doses will be administered with the TDS-IM device. All subjects will be followed until at least Day 252 (a 12 month follow-up visit may be requested). Subjects will complete post-injection memory aids for 7 days after each injection. There will also be up to 12 alternates enrolled and used to replace any original subject who fails to complete all 3 scheduled primary injections and Day 70 follow-up visit.

Inclusion Criteria:

• Healthy adult male or non-pregnant, non-lactating female, ages 18-49 (inclusive) at the time of screening
• Have provided written informed consent before screening
• Free of clinically significant health problems, as determined by pertinent medical history and clinical examination prior to entry into the study
• Available and able to participate for all study visits and procedures
• Females, if sexually active, are known to be at least one year post-menopausal (defined as no menses for 12 consecutive months), or willing to use an effective method of contraception (eg, hormonal contraception, diaphragm, cervical cap, intrauterine device, condom, anatomical sterility [self or partner]) from the date of screening until at least 3 months after the last injection
• Negative hantavirus pseudovirion neutralization assay (PsVNA) test result at screening

Exclusion Criteria:

• History or serologic evidence of prior infection with any hantavirus virus, or prior participation in a HTNV or PUUV vaccine trial

• History of severe local or systemic reactions to any vaccination or a history of severe allergic reactions

• Ongoing participation in another clinical trial

• Receipt or planned receipt of any vaccination, experimental or otherwise within the period 30 days prior to the first injection through the period 60 days after Study Day 168 (booster dose; approximately 9 month period in total), with the exception of emergency use vaccinations as needed

• Individuals in whom a skinfold measurement of the cutaneous and subcutaneous tissue for all eligible injection sites (deltoid region) exceeds 40 mm

• Individuals in whom the ability to observe possible local reactions at the eligible injections sites (deltoid region) is, in the opinion of the investigator, unacceptably obscured due to a physical condition or permanent body art

• Acute or chronic, clinically significant hematologic, pulmonary, cardiovascular, or hepatic or renal functional abnormality as determined by the investigator based on medical history, physical exam, electrocardiogram (ECG), and/or laboratory screening test

• Pregnant or lactating female, or female who intends to become pregnant during the study period

• Administration of immunoglobulins and/or any blood products within the 120 days preceding study entry or planned administration during the study period

• Any serologic evidence of hepatitis B or C infection

• Any confirmed or suspected immunosuppressive or immunodeficient condition, including human immunodeficiency virus (HIV) infection

• Administration of chronic (defined as more than 14 days) immunosuppressants or other immune modifying drugs within 6 months of study entry

  1. For corticosteroids, this will mean prednisone, or equivalent, greater than or equal to 0.5 mg/kg/day
  2. Intranasal and topical steroids are allowed

• Any chronic or active neurologic disorder, including seizures and epilepsy, excluding a single febrile seizure as a child

• Syncopal episode within 12 months of screening

• Suspected or known current alcohol and/or illicit drug abuse

• Unwilling to allow storage and use of blood for future hantavirus-related research

• Any other significant finding that in the opinion of the investigator would increase the risk of the individual having an adverse outcome from participating in this study