This is a parallel group, prospective, randomized, double-blind, two-arm, single-center study to be conducted in approximately 220 healthy participants aged 20 to 70 years who are generally healthy or with stable pre-existing health condition.~The participants should previously have their first dose of mRNA-1273. The participants, investigators, and the site personnel will be blinded to the study intervention assignment until all the participants complete their Day 29. Preparation and administration of study intervention will be performed by authorized unblinded site personnel who do not participate in the evaluation of the participants.~Eligible participants will be randomized to receive either mRNA-1273 or MVC-COV1901 vaccine at a 1:1 ratio. Randomization of participants will be stratified by the interval apart from their first dose of mRNA-1273 (< 10 weeks or ≥ 10 weeks).~The study consists of 6 on-site visits:~Day -28 to Day 1, Visit 1 (Screening) Day 1, Visit 2 (study intervention) Day 15 ± 3 days, Visit 3 Day 29 ± 3 days, Visit 4 Day 91 ± 14 days, Visit 5 Day 181 ± 14 days, Visit 6 Unscheduled visit(s) may be arranged when deemed necessary by the investigator.
The primary objective of the study is to evaluable the safety and to demonstrate the immunogenicity of heterologous prime-boost (mRNA-1273, MVC-COV1901), compared to homologous prime-boost (mRNA-1273), with an interval of 8-12 weeks, This study also assesses the safety and tolerability of the study intervention and explores the immunogenicity by the antigen-specific immunoglobulin, the immunogenicity against the VoCs, the antigen specific cellular immune response, as well as the potential efficacy of study intervention in preventing COVID-19.