The invention relates to an expression system comprising polynucleotides encoding proteins, wherein the expression system comprises a first polynucleotide encoding at least one protein, peptide or variant thereof, which induces a T cell response, and a second polynucleotide encoding at least one protein peptide or variant thereof, which induces an anti-pathogenic B cell response. The invention further relates to protein mixtures encoded by the expression system and cells comprising the expression system or the protein mixture and pharmaceutical compositions comprising the expression system or the protein mixture. The expression system, polynucleotides, proteins, cells, and pharmaceutical compositions are useful in the prophylaxis or treatment of infections. The invention further relates to nucleotide constructs which comprises, essentially consists or consists of a polynucleotide encoding a modified influenza hemagglutinin (HA).
