CSL Biotherapies (CSL) today presented preliminary conclusions from its investigations into the cause of the unexpected adverse events associated with Fluvax® influenza vaccine in 2010. The presentation was made at the Public Health Association of Australia's 13th National Immunisation Conference in Darwin.
During the influenza season of 2010, Fluvax® was associated with increased reports of fever-related (febrile) convulsions in children compared to previous seasons. The convulsions occurred predominantly in children under the age of 5 years, shortly after vaccination. The rate of febrile convulsion following administration of Fluvax® in 2010 was estimated to be 5-7 per 1,000 doses1. Fluvax® has not been licensed for use in children aged under 5 years since these events.
The preliminary conclusions have been drawn from a comprehensive two year investigation that has been monitored by the Therapeutic Goods Administration (TGA) and the Food & Drug Administration (FDA). The investigation has comprised clinical data analyses, manufacturing reviews and scientific studies.
The clinical data analyses showed Fluvax® to be associated with a higher rate of fever in children compared to at least one other licensed influenza vaccine, but that Fluvax® had not been previously linked to a significant risk of febrile convulsion2,3.
CSL's extensive manufacturing investigations, which reviewed all aspects of the manufacturing process from starting materials through to finished product, did not identify any raw material issues, process changes or deviations from the CSL standard method of manufacture that explained the increased adverse reactions in children in 2010.
CSL's preliminary conclusion is that its standard method of manufacture retains more virus components than that of other manufacturers, and that the particular characteristics of the 2010 virus components elicited an excessive immune response in some young children, triggering increased fever and fever-related convulsions.
Dr Darryl Maher, Vice-President of Medical and Research at CSL Biotherapies says, "While influenza vaccines must contain virus components to stimulate sufficient protection against influenza, it appears that components of the inactivated virus retained in Fluvax® in 2010 overstimulated the developing immune systems of some young children compared to previous seasons".
The preliminary conclusion is underpinned by comprehensive scientific studies into the virus disruption (splitting) process of CSL's method of manufacture. CSL has found in laboratory experiments that increasing the amount of splitting agent used can reduce the amount of reactive virus components in Fluvax®.
CSL is undertaking ongoing studies to understand how the characteristics of the reactive virus components in Fluvax® contributed to the adverse events in children in 2010 and to further investigate process changes that will adequately reduce them.
It will take some time to complete this work and to fully evaluate the impact and acceptability of any process modifications made. It is important that such changes not only make Fluvax® safe and effective for children, but that they also retain the current protective benefits of Fluvax® for adults and the elderly.
"The investigations have been complex because of the multiple biological factors involved. There is more work to do but we have made substantial progress in both isolating the cause of the adverse events and identifying potential process changes that will prevent them from happening again", says Dr Maher.
"Until these further studies are completed, and both CSL and the regulators are fully confident that our manufacturing process can consistently produce a safe and effective influenza vaccine for children, we will continue to fully support the age restrictions currently in place for children in all markets", says Dr Maher.
Fluvax® is not licensed for use in children aged under 5 years and is only recommended for at-risk children aged between 5 and 9 years if no other licensed influenza vaccine is available.
A recent review conducted by the Australian Technical Advisory Group on Immunisation (ATAGI) found that Fluvax® continues to have an acceptable safety profile in people aged 10 years and over. This is consistent with previous published clinical studies and CSL's ongoing global safety monitoring4,5,6.
"Influenza is a serious disease and as Australia's only on-shore manufacturer of influenza vaccine, we are committed to ensuring Fluvax® is safe and effective for all age groups", says Dr Maher.