In order to make cell culture-based influenza vaccines, frozen, preserved cells are taken from storage and grown in an incubator at 37°C. The cells are first grown in a small volume of culture medium. As the cells grow and multiply they are transferred to successively larger containers. On reaching a certain volume, influenza seed virus, obtained from the World Health Organization, is added to the cell-containing bioreactor (container) where the virus then infects the cells and multiplies, making more virus particles [2,3]. After several days the influenza virus has infected and destroyed all the cells in the bioreactor. The virus is then harvested by removing the debris made by the cells and made non-infectious, before being further purified. This purified, non-infectious solution is then blended, concentrated and filled into syringes or vials ready for use.