Evaluating the neutralizing ability of a CpG-adjuvanted S-2P subunit vaccine against SARS-CoV-2 Variants of Concern

Lien, C.-E.; Kuo, T.-Y.; Lin, Y.-J.; Lian, W.-C.; Lin, M.-Y.; Liu, L. T. C.; Chou, Y.-C.; Chen, C.

Vaccination is currently the best weapon to control the COVID-19 pandemic. However, an alarming number of novel variants termed Variants of Concern (VoC) were found to harbor mutations that diminished the neutralizing capacity of antibodies elicited by the vaccines. We have investigated the neutralizing titers of antibodies from sera of humans and rats immunized with the MVC-COV1901 vaccine against pseudoviruses coated with the wildtype, D614G, B.1.1.7, or B.1.351 spike proteins. Rats vaccinated with two doses of adjuvanted S-2P retained neutralization activities against the B.1.351 variant, albeit with a slight reduction compared to wildtype. Phase 1 vaccinated subjects showed more reduced neutralization abilities against the B.1.351 variant. The study is among the first, to our knowledge, to demonstrate dose-dependent neutralizing responses against VoCs, particularly against B.1.351, from different doses of antigen in a clinical trial for a subunit protein COVID-19 vaccine. The appearance of vaccine escape variants is a growing concern facing many current COVID-19 vaccines and therapeutics. Strategies should be adopted against the ever-changing nature of these variants. The observations of this study grant us valuable insight into preemptive strikes against current and future variants.