The present invention provides an infectious bronchitis virus (IBV) spike protein (S protein) which is based on an S protein from an IBV strain with restricted tissue tropism, but which comprises the sequence XBBXBX in the part of the S2 protein corresponding to residues 686 to 691 of the sequence given as SEQ ID No. 2, where B is a basic residue and X is any amino acid； and which comprises at least one of the following amino acid substitutions with reference to the position numbering of SEQ ID NO:2: Leucine (L) to Phenylalanine (F) at position 578 Asparagine (N) to Serine (S) at position 617 Asparagine (N) to Serine (S) at position 826 Leucine (L) to Phenylalanine (F) at position 857 and Isoleucine (I) to Valine (V) at position 1000 such that an IBV virus comprising the S protein has extended tissue tropism. The present invention also provides a virus comprising such an S protein.
