A PhD project is being undertaken by Ms Hyunsuh Kim of the International Vaccine Institute in Seoul, with the support of a grant from CSL Ltd, to address the following:
Seasonal influenza vaccines are trivalent. They contain the surface antigens of H1N1, H3N2 influenza A viruses and influenza B viruses. Most vaccines are prepared by growing these viruses in embryonated eggs.
Influenza A virus yields can be enhanced can be enhanced by selecting high-yielding reassortants. These are prepared by co-infection of eggs with a high-yielding donor strain and an epidemic strain. Reassortants can also be prepared by the application of reverse genetics.
For reasons not well understood this particular approach cannot be applied to influenza B viruses. Variability in influenza B yields is a problem for all influenza vaccine manufacturers.
Cold-adapted influenza A and B donor strains are used to prepare live attenuated intranasal vaccine viruses that grow to high titres in embryonated eggs after adaptation to growth at 25C.
It might be possible to obtain higher influenza B yields by a small number of step-wise reductions from the optimum incubation temperature of 33C.
Enhancement must be achieved with a limit of 15 passages.
The preliminary hypothesis was incorrect but other studies suggest that enhancement is possible by other approaches.
A paper outlining causes of variability has been submitted for publication was recently presented by Ms Hyunsuh Kim at the European Scientific Working Group on Influenza (ESWI) in Malta.