A Phase I, Prospective, Randomized, Open-labeled Study to Evaluate the Safety, Tolerability, and Immunogenicity of Booster Dose with MVC-COV1901 or MVC-COV1901(Beta) SARS-CoV-2 Vaccine in Adults

Abstract

Background: The use of variant-based severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccine as a booster is being evaluated to overcome reduced neutralisation of variants induced by the original SARS-CoV-2 vaccine and waning protection over time. Methods: This is a phase one, prospective, randomized, and open-labeled trial to study the safety and immunogenicity of a booster dose consisting of a subunit vaccine based on the stabilized prefusion SARS-CoV-2 spike protein, MVC-COV1901 or its Beta version, MVC-COV1901-Beta. One-hundred and seven participants aged ≥18 and <55 years, who received two or three prior doses of MVC-COV1901 vaccines, were enrolled and were to receive a booster dose of either 15 mcg of MVC-COV1901, 15 mcg or 25 mcg of MVC-COV1901-Beta in 1:1:1 ratio. The primary endpoints were the incidences of adverse events and immunogenicity of the booster dose from Visit 2 (the day of the booster) to Visit 5 (four weeks after the booster). Cellular immunity was also investigated with memory B cell (MBC) and T cell assays. Findings: Adverse reactions after either MVC-COV1901 or MVC-COV1901-Beta booster doses after two or three doses of MVC-COV1901 were comparable and mostly mild and transient. At four weeks after the booster dose, participants with two prior doses of MVC-COV1901 exhibited numerically higher levels of neutralising antibodies against SARS-CoV-2 or Beta variant than participants with three prior doses of MVC-COV1901 regardless of the type of booster used. However, compared to 15 mcg of MVC-COV1901, 25 mcg of MVC-COV1901-Beta significantly improved neutralising antibody titre against Beta variant and BA.4/BA.5 Omicron variant pseudoviruses. The booster dose also significantly increased the proportion of spike-specific MBCs, including those of Beta and Omicron variants. Interpretation: MVC-COV1901-Beta can be effectively used as a booster dose against SARS-CoV-2, including the circulating BA.4/BA.5 Omicron variant.