Hypothesis: A booster dose of naked (i.e. non-adjuvanted) AKS-452 vaccine will provide an enhanced immune response after vaccination with any of the registered vaccines against COVID-19.~Primary objective: To determine the immunogenicity 4-6 weeks after subcutaneous injection of a booster dose of AKS-452X vaccine given at >=3 months post-initial vaccination (i.e. Pfizer [ Comirnaty], Moderna [Spikevax], Janssen [Ad26.COV2.S], AstraZeneca [Vaxzevria]) in human healthy volunteers.~Secondary objective: Vaccine safety and side effects after booster vaccination. Follow-up will occur for up to 9 months post-study vaccine.~Study design: Single center, open-label, safety and efficacy study on the biological activity of a SP/RBD-Fc antigen booster vaccine (AKS-452X) against COVID-19.~Study population: Healthy human volunteers, 18 - 85 years, having received a registered vaccine (i.e. Pfizer [Comirnaty], Moderna [Spikevax], Janssen [Ad26.COV2.S], AstraZeneca [Vaxzevria]).~Intervention: One booster dose-level of naked AKS-452 (90 µg) administered via s.c. route in 150 subjects per cohort in which safety parameters and neutralizing IgG titers will be reviewed after the booster dose of 90 µg s.c.. Enhanced immune response is defined as: i) seroconversion based on a true positive based on the SP/RBD IgG ELISA assay positive/negative cutoff criteria using the quantitative cut-off value defined by the assay kit batch expressed in μg/mL. The positive/negative cutoff value was established as 2.42 µg/mL from the validation analysis for the current lot of assay kits, but it should be noted that for each new lot of assay kits, Akston QC performs a re-validation of the cutoff value in order to maintain clinical agreement from lot-to-lot, ii) two times (2x) the baseline SP/RBD IgG at day 56 after a boostering, as compared to the titer at the time of screening.~Main study parameters/endpoints: Primary endpoint: The percentage of patients that i) achieve an SP/RBD-specific IgG antibody titer level of ≥ 2.42 µg/mL at the day 28 time-point post-intervention (i.e. booster vaccine) if the base-line value prior to receiving the booster vaccine was < 2.42 µg/mL or ii) where the SP/RBD-specific IgG antibody titer is at least 2x the base-line value prior to receiving the booster vaccine if the base-line value prior to receiving the booster vaccine was ≥ 2.42 µg/mL. The percentage of patients in each of the four cohorts that achieve the primary endpoint threshold at 28 days post-intervention will be calculated (n (%)). Secondary endpoint: Safety evaluation in the four cohorts for local and systemic adverse events after injection at each pre-defined scheduled follow-up (at 28, 56, 91, 182 and 238 days post intervention). Patients will continue to be followed passively for additional safety events out to 9 months post-intervention.
Aim: To investigate if a subcutaneous (s.c.) booster dose of 90 µg of the naked Akston AKS-452 vaccine (AKS-452X) at >= 3 months post initial vaccination, with any of the four registered vaccines, will boost the antibody titer and immune response in human healthy volunteers 4-6 weeks after s.c. injection.