In accordance with its mandate to provide guidance to Member States on health policy matters, WHO issues a series of regularly updated position papers on vaccines and vaccine combinations against diseases that have an international public health impact. These papers are concerned primarily with the use of vaccines in large-scale immunization programmes; limited vaccination, as executed mostly in the private sector, may be a valuable supplement to national programmes, but is not emphasized in these policy documents. The position papers summarize essential background information on the respective diseases and vaccines, and conclude with the current WHO position concerning their use in the global context. The papers have been reviewed by a number of experts inside and outside WHO, and are designed for use mainly by national public health officials and immunization programme managers. However, the position papers may also be of interest to international funding agencies, the vaccine manufacturing industry, the medical community and the scientific media. This position paper is concerned mainly with seasonal (epidemic) influenza and the public health impact of yearly influenza vaccination.2