Simian adenoviral vectors with two expression cassettes

A simian adenoviral vector comprising two expression cassettes, wherein each expression cassette comprises a transgene and a promoter, and wherein the first expression cassette is inserted in the E1 region of the simian adenoviral vector, and the second expression cassette is inserted in a region of the adenoviral vector that is compatible with vector replication;

• the transgene of the first and second expression cassettes encode an antigen;
• and the first expression cassette and/or the second expression cassette comprises an enhanced human CMV promoter having a nucleic acid sequence having at least about 90% sequence identity to SEQ ID NO:
• 6.