Abstract: A nucleic acid molecule including a translation control element having a translation initiation activity and a coding region operably linked to the translation control element and encoding an immunogen of an influenza virus or a severe fever with thrombocytopenia syndrome virus (SFTSV) or fragments thereof is disclosed. The nucleic acid molecule or an expression system where the nucleic acid molecule is inserted can be used in a pharmaceutical composition for treating or preventing influenza or SFTS, for example, that an mRNA vaccine or a gene therapy platform.