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

Perez-Rodriguez, S.; Rodriguez-Gonzalez, M. d. l. C.; Ochoa-Azze, R.; Climent-Ruiz, Y.; Gonzalez-Delgado, C. A.; Paredes-Moreno, B.; Valenzuela-Silva, C.; Rodriguez-Noda, L.; Perez-Nicado, R.; Gonzalez-Mugica, R.; Martinez-Perez, M.; Sanchez-Ramirez, B.; Hernandez-Garcia, T.; Diaz-Machado, A.; Tamayo-Rodriguez, M.; Martin-Trujillo, A.; Rubino-Moreno, J.; Suarez-Batista, A.; Dubed-Echevarria, M.; Perez-Guevara, M. T.; Amoroto-Roig, M.; Chappi-Estevez, Y.; Bergado-Baez, G.; Pi-Estopinan, F.; Chen, G.-W.; Valdes-Balbin, Y.; Garcia-Rivera, D.; Verez-Bencomo, V.

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 1 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 mcg d-RBD plus outer membrane vesicles from N. meningitidis); 2) FINLAY-FR-1A-50 mcg d-RBD (three doses); 3) FINLAY-FR-1A-25 mcg 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 of 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 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.