Evaluating the efficacy and safety of SpikoGen®, an Advax-CpG55.2–adjuvanted severe acute respiratory syndrome coronavirus 2 spike protein vaccine: a phase 3 randomized placebo-controlled trial

Objectives: We sought to investigate the efficacy and safety of SpikoGen®, a subunit coronavirus disease 2019 (COVID-19) vaccine composed of a recombinant severe acute respiratory syndrome coronavirus 2 spike protein with Advax-CpG55.2™ adjuvant.

Methods: This randomized, placebo-controlled, double-blind, phase 3 trial was conducted on 16 876 participants randomized (3:1) to receive two intramuscular doses of SpikoGen® or a saline placebo 21 days apart. The primary outcome was to assess the efficacy of SpikoGen® in preventing symptomatic COVID-19. Secondary outcomes included safety assessments and evaluation of SpikoGen® vaccine's efficacy in preventing severe COVID-19. The study aimed for 147 COVID-19 symptomatic cases.

Results: Overall, 12 657 and 4219 participants were randomized to the SpikoGen® and placebo group and followed for a median of 55 days (interquartile range, 48–60 days) and 51 days (interquartile range, 46–58 days) after 14 days of the second dose, respectively. In the final per-protocol analysis, the number of COVID-19 cases was 247 of 9998 (2.4%) in the SpikoGen® group and 119 of 3069 (3.8%) in the placebo group. This equated to a vaccine efficacy of 43.99% (95% CI, 30.3–55.0%). The efficacy was calculated to be 44.22% (95% CI, 31.13–54.82%) among all participants who received both doses. From 2 weeks after the second dose, 5 of 9998 (0.05%) participants in the SpikoGen® group and 6 of 3069 (0.19%) participants in the placebo group developed severe COVID-19, equating to a vaccine efficacy against severe disease of 77.51% (95% CI, 26.3–93.1%). The SpikoGen® vaccine was well tolerated.

Discussion: A 2-dose regimen of SpikoGen® reduced the rate of COVID-19 and severe disease in the wave of the Delta variant.