The values of other 9 samples could not be assessed because of the leaking and broken blood specimen containers. 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%C53.51%) to anti-S1 and 29.41% (95% CI, 13.27%C46.57%) 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 IgG2a Isotype Control antibody (FITC) a single-center study, and it will be important for future large multicenter studies to extend these results to other immunocompromised patient groups. Keywords: SpikoGen, Kidney transplant, Booster dose, COVID-19, SARS-CoV-2 Introduction As of September 2022, SARS-CoV-2 is still infecting many people worldwide, with vaccination playing an important role in helping to reduce the 2-Methoxyestrone burden of disease. However, the problems of rapidly waning immunity after vaccination as well as immune escape caused by new variants, including B.1.617 or B.1.1.529, have led to calls for booster vaccinations to restore waning immunity and protection. Low rates of seroconversion have been reported in solid organ transplant recipients receiving mRNA SARS-CoV-2 vaccines.1 , 2 In a study of BNT162b2 on renal transplant recipients, a third vaccine dose led to induction of neutralizing antibodies in populations with and without response to the primary vaccination.3 In another study, a third dose of BNT162b2 restored neutralizing titers of antiCreceptor-binding domain antibodies in 40% of participants who had not responded to the previous vaccination course.4 On the basis of all the positive findings, a meta-analysis has also recommended a third dose of mRNA vaccines in patients with solid organ transplants, considering its enhanced effects of immunogenicity and acceptable safety profile.5 SpikoGen is an adjuvanted recombinant S protein trimer vaccine that induces strong humoral and cellular responses in previous Phase II and a pivotal Phase III trials, indicating positive tolerability, immunogenicity, and efficacy, resulting in emergency use authorization from Iran’s Food and Drug Administration in October 2021.6 Because patients under immunosuppressive therapy were excluded from the previous SpikoGen clinical trials, its immunogenicity and tolerability have not previously been assessed in this population. Hence, this study aimed to investigate the immunogenicity and safety of a SpikoGen booster shot in patients undergoing kidney transplant who are receiving immunosuppressive therapy and had previously received primary vaccination with 2 doses of an inactivated 2-Methoxyestrone whole virus platform (Sinopharm) vaccine. Methods Setting This study was a single-arm, open-label, prospective clinical trial conducted in 43 patients during February and March 2022 at Shahid Labbafinezhad clinic, affiliated with Shahid 2-Methoxyestrone Beheshti University of Medical Sciences, Tehran, Iran, which is considered a referral center for kidney transplantation in Iran. Patients Patients undergoing renal transplant who were 18 years and older were eligible to enter the study if they had received a primary course of vaccination with Sinopharm vaccine 1 to 3 months earlier. The exclusion criteria were as follows: pregnant or lactating women; patients with active infection or symptoms of COVID-19 at the screening visit; history of COVID-19 between the primary vaccination and the third booster dose; active cytomegalovirus infection; history of receiving rituximab or intravenous immunoglobulin during the past 6 months; patients with a history of severe allergic reactions (eg, anaphylaxis) to.