The structures of immunogens that elicit the most potent neutralization antibodies to prevent COVID-19 infection are still under investigation . In this study, we tested the efficacy of a recombinant trimeric Spike protein containing polyI: C (PIKA) adjuvant in mice immunized by a 0–7–14 day schedule . The results showed that a Spike protein-specific antibody was induced at Day 21 with titer of above 50,000 on average, as measured by direct binding . The neutralizing titer was above 1000 on average, as determined by a pseudo-virus using monoclonal antibodies (40592-MM57 and 40591-MM43) with IC50 at 1 μg/mL as standards . The protein/peptide array-identified receptor-binding domain (RBD) was considered as immunodominant . No linear epitopes were found in the RBD, although several linear epitopes were found in the C-terminal domain right after the RBD and heptad repeat regions . Our study supports the efficacy of a recombinant trimeric Spike protein vaccine candidate for COVID-19 that is safe and ready for storage and distribution in developing countries.