The replacement of uridine by 1-methylpseudouridine helped mRNA vaccines against COVID-19 to achieve significantly improved pharmacological properties. However, the limited shelf life and laborious formulation in liposomes complicate the production and presumably on the efficiency of mRNA vaccines. It can be expected that further modifications will allow considerable optimizations. The focus of this project is the advancement and use of chemical modification of nucleotide positions of the mRNA (based on click chemistry) as well as the generation of polycistronic mRNAs in order to be able to vaccinate against co-existing virus variants with the aid of a single vaccine.