An antigen concentration procedure does not involve lyophilisation of a bulk antigen before its final formulation and/or delivery. Thus a process for preparing a vaccine comprises steps of (i) increasing the concentration of an antigen in a liquid composition including that antigen, to provide a concentrated antigen, and (ii) formulating a vaccine from the concentrated antigen. The concentrated antigen is not lyophilised between or during steps (i) and (ii). The invention is particularly useful for preparing solid vaccine forms.
