Immunogenicity and Safety of SpikoGen, an Adjuvanted Recombinant SARS-CoV-2 Spike Protein, as a Heterologous Third Booster Dose in Kidney Transplant Patients: A Single-arm Clinical Trial

PURPOSE: Studies have found that immunocompromised patients have suboptimal responses to COVID-19 vaccines, leading to approval of a need for booster doses in this population. SpikoGen® is a subunit recombinant spike protein vaccine combined with Advax-CpG55.2™ adjuvant to protect against COVID-19. Previous clinical trials found this vaccine to be tolerable, immunogenic, and efficacious in reducing the risk of COVID-19, including severe disease. However, the effects of this vaccine have not been assessed in immunocompromised patients. This study sought to assess the immunogenicity and safety of the SpikoGen vaccine as a third booster dose in patients undergoing kidney transplant who were receiving immunosuppressive therapy and had received their primary vaccination based on an inactivated whole virus platform (Sinopharm). METHODS: This single-arm trial was performed with 43 patients undergoing kidney transplant. The participants received a single booster dose of the SpikoGen vaccine 1 to 3 months after primary vaccination with 2 doses of the Sinopharm vaccine. Immunogenicity assessments were performed at baseline and 30 days after the booster dose. The primary outcomes were seroconversion rates of anti-S(1) and surrogate virus neutralizing antibodies. Safety outcomes included the incidence of solicited and unsolicited adverse events in the 7 days and 1 month after the booster dose, respectively. FINDINGS: The SpikoGen vaccine induced positive humoral and cellular responses 30 days after the booster dose in those patients who were seropositive or seronegative after 2 primary doses of the Sinopharm vaccine. Thirty days after the SpikoGen vaccine booster, seroconversion rates were 35.29% (95% CI, 19.75%–53.51%) to anti-S(1) and 29.41% (95% CI, 13.27%–46.57%) to surrogate neutralizing antibodies. The most common local and systemic reported solicited adverse events were injection site pain and fatigue, which were largely mild and transient. No serious adverse events were reported. IMPLICATIONS: A single booster dose of SpikoGen vaccine given 1 to 3 months after primary vaccination with 2 doses of Sinopharm vaccine induced positive humoral and cellular immune responses in immunosuppressed patients undergoing renal transplant, thereby achieving spike antibody levels predictive of protection. This study was performed as a single-center study, and it will be important for future large multicenter studies to extend these results to other immunocompromised patient groups.