A process for preparing a lyophilised vaccine antigen, comprising steps of (i) increasing the concentration of an antigen in a liquid composition including that antigen using centrifugal filtration and/or ultrafiltration, to provide a concentrated antigen, and (it) lyophilising the concentrated antigen, to provide the lyophilised vaccine antigen. The lyophilised material can be reconstituted and used for vaccine formulation. The process is particularly useful with influenza vaccine antigens.
