Considering that the expression level of the S1 protein is much higher than that of the RBD (Mamedov et al., 2021a) or N+RBD variants (Mamedov et al., 2021b), plant-produced S1 subunits of SARS-CoV-2 could be cost-effective and a safe protein-based vaccine candidate against COVID-19 variants. The gene discussed is PSMD1; the disease is COVID-19.