A method for synthesizing influenza virus-like particles (VLPs) within a plant or a portion of a plant is provided. The method involves expression of influenza HA of type A/California/04/09 in plants and the purification by size exclusion chromatography. The invention is also directed towards a VLP comprising influenza HA protein of type A/California/04/09 and plants lipids. The invention is also directed to a nucleic acid encoding influenza HA of type A/California/04/09 as well as vectors. The VLPs may be used to formulate influenza vaccines, or may be used to enrich existing vaccines.
