A stockpile is a special vaccine reserve to be used in emergencies (i.e. supply disruptions or disease outbreaks). As older vaccines approach their expiration date they are replaced with fresh vaccines and are rotated into the market for use in campaigns and routine immunization. In 2002, the GAVI Board approved the establishment of a Yellow Fever (YF) vaccine stockpile for outbreak response and to be used for preventive campaigns. The approval was for 6 million doses each year for an initial period of 3 years.