An inactivated influenza virus preparation is described which comprises a haemagglutinin antigen stabilised in the absence of thiomersal, or at low levels of thiomersal, wherein the haemagglutinin is detectable by a SRD assay. The influenza virus preparation may comprise a micelle modifying excipient, for example &alpha-tocopherol or a derivative thereof in a sufficient amount to stabilise the haemagglutinin.
