The present invention provides a recombinant soluble trimeric hemagglutinin (rHA) protein comprising a hemagglutinin ectodomain and an oligomerization domain. The rHA is produced as a soluble homotrimer, and may further comprises a signal peptide and/or an endoplasmic reticulum (ER) retention signal. The invention is also directed to nucleic acids encoding the rHA of the invention, as well as vectors and chimeric constructs comprising the nucleic acid. Methods of producing the rHA are also provided. The rHA described herein may be used to formulate influenza vaccines, or may be used to enrich existing vaccines.
