Two or more Neisserial proteins are joined such that they are translated as a single polypeptide chain. Hybrid proteins are represented by the formula NH2-A-[-X-L-]n-B—COOH where X is an amino acid sequence, L is an optional linker amino acid sequence, A is an optional N-terminal amino acid sequence, B is an optional C-terminal amino acid sequence, and n is an integer greater than I. Proteins where each of the n-X— moieties shares sequence identity to each other —X— moiety, the protein is a ‘tandem protein’.