The invention contemplates a new synthetic, codon-optimized Puumala virus (PUUV) full-length M gene open reading frame (ORF) that encodes a unique consensus amino acid sequence. The PUUV ORF was cloned into a plasmid to form the first stable PUUV full-length M gene that elicits neutralizing antibodies. The gene can be engineered into a molecular vaccine system, and is useful to protect mammals against infection with Puumala virus.