This is an open-label, dose-ranging, study to evaluate the safety and immunogenicity of the investigational HDT-301 vaccine in healthy (vaccinated or unvaccinated) adult subjects, with a 4:3 recruitment of individual aged 18-49 years and 50-65 years, respectively. The study duration is approximately 13 or 14 months for each subject.~Three cohorts of 21 subjects each will be sequentially recruited in the study:~Cohort 1 will include individuals with vaccination against COVID-19 who will receive a two-dose schedule of HDT-301 56 days apart.~Cohort 2 will include individuals with vaccination against COVID-19 who will receive a one-dose schedule of HDT-301.~Cohort 3 will include individuals with no history of vaccination against COVID-19 who will receive a two-dose schedule of HDT-301 56 days apart.~Recruiting and screening of participants will be conducted on a continual basis. Subjects confirmed to be Emergency Use Authorization (EUA) SARS-CoV-2 vaccine recipients will first be placed into either Cohort 1 (Study Days 1 and 57; Two-Dose Regimen) or Cohort 2 (Study Day 1; One-Dose Regimen) then subsequently placed into each of the three dose groups. Subjects in the Cohort 3 (naïve, unimmunized) subset will be placed into each of the three dose groups to receive the study vaccine on Study Days 1 and 57 (Two-Dose Regimen). Each cohort will be divided into 3 groups of 7 participants, that will be provided HDT-301 at either a low-, mid- or high-dose. For each of the three-dose groups, a sentinel group will be initially enrolled and followed through Day 8 post-dose one for safety. If no halting rules are met by Day 8 enrollment will proceed to the remaining subjects. Blood samples will be collected during the study for each participant.
This is Phase 1 study is to assess tolerability and immunogenicity of three dose levels of the investigational HDT-301 vaccine administered intramuscularly (IM), both in immunization-naïve participants and as a booster for those participants who previously received a SARS-CoV-2 vaccine.~Safety and tolerability will be the primary endpoint assessed by incidence of adverse events at each dose through 12 months after completion of the vaccination regimen (either one dose, or two doses provided 56 days apart). Immunogenicity evaluations will be conducted for pre-specified timepoints as secondary and exploratory endpoints.