Currently, the steps performed prior to release of influenza strains to vaccine manufacturers involve passaging influenza virus through eggs. The invention aims to provide procedures useful in manufacturing influenza vaccines, in which the use of eggs is reduced, and preferably is avoided altogether. For instance, rather than use chicken eggs for influenza vaccine isolation, MDCK cells (Madin Darby canine kidney cells) may be used e.g. growing in suspension, growing in a serum-free medium, growing in a protein-free medium, being non-tumorigenic, grown in the absence of an overlay medium, etc.
