The Effect of the Anti-Covid-19 Vaccine Abdala Dose Level and Dosing Interval in Rats and Cynomolgus Monkeys

Several anti-Covid-19 vaccines have been developed corresponding to at least 11 vaccine platforms, including novel technology. The Abdala vaccine is based on the RBD fragment of the surface antigen of SARS-CoV-2 expressed in yeast. Previously, we demonstrated the immunogenicity of the recombinant antigen in animals. The present studies examined the impact of Abdala vaccination on the production of RBD-specific antibodies and their functional capacity using two immunization schedules (short 0-14-28 versus long 0-21-42) and two dose levels (10 and 50 μg) in rats and monkeys. The functional capacity of the antibody response was evaluated using an in vitro test to detect blocking antibodies to the ACE-2-RBD interaction and neutralizing activity versus the homologous Wuhan strain. For monkey sera, neutralization against variants of concern (VOC) beta (B.1.351), delta (B.1.617.2) and omicron (BA.1) was also evaluated. Taken together, the findings revealed previously unappreciated differences of the Abdala vaccine in the functional capacity of the antibody response according to the number of inoculations, the dose level, and the dose interval. In this regard, when using the short dose interval, three inoculations seem necessary to improve the functional antiviral response which is also favored with the higher dose level and a long dosing interval. The results in the NHP model also suggest that two doses using a long time interval (0-21) could improve the efficacy of the Abdala vaccine compared to the short-interval regime (0-14). Cross-neutralization against variants of concern was also demonstrated.