This EMA guideline lays down the quality recommendations the cells used to isolate candidate influenza vaccine viruses, the conditions in which to which the viruses are isolated and the subsequent purification and development of master seed batches and GMP conditions.

This guidance considers the different technologies available and that are in wide use and makes a series of recommendations. Manufactures still need to consider which are most appropriate for their products.

excerpt from guidance

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This Guideline lays down the quality recommendations for cells used to isolate candidate influenza vaccine viruses, the conditions under which the viruses are isolated and the subsequent passage of the
viruses until the manufacturer’s Master Seed is prepared under GMP conditions.

Many influenza vaccine manufacturers are developing cell culture processes for the production of inactivated vaccine using a variety of cell types and several such vaccines have been licensed within the EU. Manufacturers of cell-derived vaccine typically use the recommended egg-derived candidate vaccine virus to derive their seed virus; this may be the wild type egg isolate or a high growth reassortant (hgr), especially for influenza A viruses. There is currently no published evidence that the use of an egg-derived hgr provides a growth advantage in cells compared with the wild type eggderived recommended strain – it is simply the vaccine virus that is available from WHO collaborative laboratories that supply such viruses.
Manufacturers of cell-derived influenza vaccine may prefer to use a cell-only passaged virus instead of one that has been egg-adapted. This is because research indicates that when a human influenza virus is adapted to grow in eggs, it undergoes phenotypic changes that might include changes to its antigenicity/immunogenicity [1]. Virus isolated on mammalian cell cultures do not, attheleast initially, undergo the type of selection that occurs during initial passage in eggs and typically the haemagglutinin (HA) of a cell isolated virus is structurally more related to the virus found in clinical specimens in contrast to egg-adapted variants in which specific HA amino acid substitutions have been identified [1]. Thus a cell-isolated virus might be more clinically relevant for vaccine than an egg isolate although to date this has not been fully demonstrated scientifically. For the reasons mentioned above, manufacturers are now keen to use non-egg adapted viruses, which are antigenically closer to the wild type virus. However, cells in general use by National Influenza Centres and WHO Collaborating Centres for virus isolation are not qualified/validated for use in deriving a candidate vaccine virus and so currently only egg-isolated viruses are taken forward as vaccine candidates.

The major concern in isolating vaccine viruses in cells is the possibility of adventitious agent contamination that might derive from the cells, the environment or materials used during isolation and propagation of the viruses. Thus, the purpose of this document is to provide regulatory guidance on the quality of the cells used to isolate the virus, the conditions under which viruses are isolated and the subsequent passage of these viruses until the manufacturer’s master seed is prepared according to GMP. Normally, regulatory guidance is directed towards the vaccine manufacturers as it is they who have the responsibility for ensuring that their vaccine seed is suitable for the production of a human influenza vaccine. However, it is appreciated that the isolation of influenza candidate vaccine viruses will take place in WHO Collaborating Centres and as such, from a practical point of view, these laboratories should be familiar with the EU recommendations presented in this document. The quality aspects of the establishment of a manufacturer’s Master Seed lot and subsequent use in a cell vaccine manufacturing process have been described previously in the guideline ‘Cell Culture Inactivated Influenza Vaccines, Annex to note for guidance on harmonisation of requirements for influenza vaccines’ [2] and will not be further addressed in this document.