Safety and immunogenicity of anti-SARS CoV-2 vaccine SOBERANA 02 in homologous or heterologous scheme: Open label phase I and phase IIa clinical trials.

BACKGROUND: SOBERANA 02 is a COVID-19 vaccine based on SARS-CoV-2 recombinant RBD conjugated to tetanus toxoid (TT). SOBERANA Plus antigen is dimeric-RBD. Here we report safety and immunogenicity from phase I and IIa clinical trials using two-doses of SOBERANA 02 and three-doses (homologous) or heterologous (with SOBERANA Plus) protocols. METHOD: We performed an open-label, sequential and adaptive phase I to evaluate safety and explore the immunogenicity of SOBERANA 02 in two formulations (15 or 25 µg RBD-conjugated to 20 µg of TT) in 40 subjects, 19-59-years-old. Phase IIa was open-label including 100 volunteers 19-80-years, receiving two doses of SOBERANA 02-25 µg. In both trials, half of volunteers were selected to receive a third dose of the corresponding SOBERANA 02 and half received a heterologous dose of SOBERANA Plus. Primary outcome was safety. The secondary outcome was immunogenicity evaluated by anti-RBD IgG ELISA, molecular neutralization of RBD:hACE2 interaction, live-virus-neutralization and specific T-cells response. RESULTS: The most frequent adverse event (AE) was local pain, other AEs had frequencies ≤ 5%. No serious related-AEs were reported. Phase IIa confirmed the safety in 60 to 80-years-old subjects. In phase-I SOBERANA 02-25 µg elicited higher immune response than SOBERANA 02-15 µg and progressed to phase IIa. Phase IIa results confirmed the immunogenicity of SOBERANA 02-25 µg even in 60-80-years. Two doses of SOBERANA02-25 µg elicited an immune response similar to that of the Cuban Convalescent Serum Panel and it was higher after the homologous and heterologous third doses. The heterologous scheme showed a higher immunological response. Anti-RBD IgG neutralized the delta variant in molecular assay, with a 2.5-fold reduction compared to D614G neutralization. CONCLUSIONS: SOBERANA 02 was safe and immunogenic in persons aged 19-80 years, eliciting neutralizing antibodies and specific T-cell response. Highest immune responses were obtained in the heterologous three doses protocol. TRIAL REGISTRY: https://rpcec.sld.cu/trials/RPCEC00000340, https://rpcec.sld.cu/trials/RPCEC00000347.

A randomized, double-blind phase I clinical trial of two recombinant dimeric RBD COVID-19 vaccine candidates: Safety, reactogenicity and immunogenicity.

BACKGROUND: The Receptor Binding Domain (RBD) of the SARS-CoV-2 spike protein is the target for many COVID-19 vaccines. Here we report results for phase I clinical trial of two COVID-19 vaccine candidates based on recombinant dimeric RBD (d-RBD). METHODS: We performed a randomized, double-blind, phase I clinical trial in the National Centre of Toxicology in Havana. Sixty Cuban volunteers aged 19-59 years were randomized into three groups (20 subjects each): 1) FINLAY-FR-1 (50 µg d-RBD plus outer membrane vesicles from N. meningitidis); 2) FINLAY-FR-1A-50 (50 µg d-RBD, three doses); 3) FINLAY-FR-1A-25 (25 µg d-RDB, three doses). The FINLAY-FR-1 group was randomly divided to receive a third dose of the same vaccine candidate (homologous schedule) or FINLAY-FR-1A-50 (heterologous schedule). The primary outcomes were safety and reactogenicity. The secondary outcome was vaccine immunogenicity. Humoral response at baseline and following each vaccination was evaluated using live-virus neutralization test, anti-RBD IgG ELISA and in-vitro neutralization test of RBD:hACE2 interaction. RESULTS: Most adverse events were of mild intensity (63.5%), solicited (58.8%), and local (61.8%); 69.4% with causal association with vaccination. Serious adverse events were not found. The FINLAY-FR-1 group reported more subjects with adverse events than the other two groups. After the third dose, anti-RBD seroconversion was 100%, 94.4% and 90% for the FINLAY-FR-1, FINLAY-FR-1A-50 and FINLAY-FR-1A-25 respectively. The in-vitro inhibition of RBD:hACE2 interaction increased after the second dose in all formulations. The geometric mean neutralizing titres after the third dose rose significantly in the group vaccinated with FINLAY-FR-1 with respect to the other formulations and the COVID-19 Convalescent Serum Panel. No differences were found between FINLAY-FR-1 homologous or heterologous schedules. CONCLUSIONS: Vaccine candidates were safe and immunogenic, and induced live-virus neutralizing antibodies against SARS-CoV-2. The highest values were obtained when outer membrane vesicles were used as adjuvant. TRIAL REGISTRY: https://rpcec.sld.cu/en/trials/RPCEC00000338-En.