A synthetic DNA vaccine against SARS-CoV-2 infection comprises a codon-optimized coding sequence for optimal mammalian expression of a pSARS2 spike glycoprotein (pSARS2-S). The signal peptide may be replaced with the signal peptide from the human IgG2 heavy chain. Systemic S1-specific IgG antibodies and neutralizing antibodies (nAbs) were significantly induced in mice at 2 weeks-post three injections with 100 μg of the pSARS2-S vaccine via intramuscular (IM) needle injection. IM immunization induced Th1-skewed and long-lasting IgG response in BALB/c mice. Immunogenicity and induction of nAbs were enhanced with a needle-free delivery system, wherein two doses were sufficient to elicit significant levels of systemic S1-specific IgG antibodies and nAbs via IM or intradermal immunization.