\[Part A\] Part A is open-label, dose-ranging study, enrolling total of 40 subjects. Part A is divided into two arm, low dose (Group 1) and high dose (Group 2). The subjects will be contacted by telephone to report adverse events or other reactions the day following the first vaccination. Once these first five subjects in Group 1 complete the Week 1 visit, all available clinical laboratory and adverse event data will be reviewed by the Data Safety Monitoring Board (DSMB). Further enrollment into Group 1 will be paused during this DSMB review. If DSMB determines there are no safety findings judged to be of clinical concern and no dose limiting toxicities nor any stopping events observed, enrollment will be opened for the remaining subjects in Group 1. Once Group 1 enrollment is completed \[i.e., 20 total subjects enrolled\], Group 2 will open to enrollment. Daily safety assessment of all enrolled subjects will be supported by the Study Medical Monitor on an ongoing basis while the first five subjects are being enrolled, if needed. The subjects will be contacted by telephone to report adverse events or other reactions the day following the first vaccination. Once the first five subjects Group 2 complete the Week 1 visit, all available clinical laboratory and adverse event data from these first five subjects, along with the safety data from subjects in Group 1, will be reviewed by the DSMB. However, enrollment may continue while this DSMB review is conducted, without any pause to enrollment of the remaining subjects in Group 2.

Once all subjects in Part A Group 1 and Group 2 complete the Week 8 visit, all available clinical laboratory, adverse event, immunogenicity data from all subjects will be reviewed by the DSMB. The DSMB will additionally review serious adverse events (SAEs) and adverse events of special interest (AESIs) date throughout the study. With DSMB's recommendation, the optimal dose for Part B will be selected by the Sponsor based on the following criteria which may be adjusted over the course of the study. Percentage immunogenic seroconversionRelative immunogenicity between INO-4800 Study Arms (Low dose vs. High dose)Safety profile of each INO-4800 Study Arms (Low dose vs. High dose). All subjects will be followed for 48 weeks following the 2nd vaccination. Week 52 will be the End of Study (EOS) visit.

\[Part B\] Part B is divided into two arm, IP Arm (Group 3) and Placebo Arm (Group 4). Part B will be randomized, double-blind, placebo-controlled trial, enrolling 60 subjects in IP arm, and 20 subjects in Placebo arm in 19-50 age group, and 30 subjects in IP arm, and 10 subjects in Placebo arm in 51-64 age group, for total of 90 subjects in IP arm, and 30 subjects in Placebo arm. At dosing visit, subjects will be randomized to either Group 3 or Group 4. The subjects will be contacted by telephone to report adverse events or other reactions the day following the first vaccination. DSMB review of safety findings will be performed according to the DSMB charter. All subjects will be followed for 48 weeks following the 2nd vaccination. Week 52 will be the End of Study (EOS) visit.Should the criteria for any dose limiting toxicity or stopping rule be met, at any time, further enrollment and administration of INO-4800 will be paused for further evaluation. The Sponsor will consult the DSMB, if needed, to determine whether to enroll and/or dose the remainder of the subjects. All subjects will be followed for 48 weeks following the 2nd vaccination. Week 52 will be the End of Study (EOS) visit.