Compositions and methods are provided for potent mRNA vaccines for prevention and treatment of 2019 novel Coronavirus (2019-nCoV) infections. The compositions include a pharmaceutical composition containing one or more mRNA molecules encoding spike protein epitopes, including mutated epitopes, or mRNA cocktails that encode critical viral genes together with pharmaceutically acceptable polymeric nanoparticle carriers and liposomal nanoparticle carriers. Methods for stimulating system immune responses and treatment are provided, including subcutaneous, intraperitoneal and intramuscular injections.