The present invention relates to a synthetic plant-optimized nucleic acid molecule having a Norwalk virus capsid protein coding nucleotide sequence, and nucleic acid constructs, host cells, expression systems, and plants having the plant-optimized Norwalk virus nucleic acid molecule. The present invention also relates to a method of producing Norwalk virus capsid protein virus-like particles in a transgenic plant or transgenic plant seed transformed with a plant-optimized nucleic acid molecule encoding Norwalk virus capsid protein. The plant or a component thereof can be administered to a subject under conditions effective to immunize the subject against disease resulting from infection by a Norovirus, including Norwalk virus. An oral vaccine for immunization of a subject against Norwalk virus infection is also disclosed.