The present invention relates to mRNAs suitable for use as mRNA-based vaccines against infections with MERS coronaviruses. Additionally, the present invention relates to a composition comprising the mRNAs and the use of the mRNAs or the composition for the preparation of a pharmaceutical composition, especially a vaccine, e.g. for use in the prophylaxis or treatment of MERS coronavirus infections. The present invention further describes a method of treatment or prophylaxis of infections with MERS coronavirus using the mRNA sequences.