Disclosed are recombinant spike ectodomain proteins, compositions, vectors, kits, and methods for inducing an immune response against avian infectious bronchitis virus (IBV). In particular, the recombinant proteins, compositions, vectors, kits, and methods relate to, include, and/or utilize a soluble, multimerized form of the (IBV) spike (S) protein ectodomain. The recombinant proteins, compositions, vectors, kits, and methods may be utilized to immunize poultry against disease associated with IBV infection or to protect poultry from IBV infection.