Virus traces in Fluvax blamed for risk in children

CSL (ASX:CSL) unit CSL Biotherapies has tentatively blamed the particulars of the manufacturing process for the adverse reactions to its Fluvax influenza vaccine in some young children in 2010.

A two-year investigation into the association between Fluvax and increased risks of febrile convulsion in children under the age of five has pinned the preliminary blame on the number of virus components remaining in the vaccine.

During the 2010 flu season, Fluvax was associated with fever-related convulsions in young children, occurring shortly after vaccination, at an estimated rate of 5-7 per 1,000 doses.

Since the incidences, Fluvax has not been licensed for use in children younger than five, and is only recommended in children aged 5-9 if no other licensed flu vaccine is available.

But the Australian Technical Advisory Group on Immunisation has reviewed Fluvax and determined it has an acceptable safety program in children aged 10 years or older.

The investigation, which combined clinical data analyses, manufacturing reviews and scientific studies, did not identify any changes in the manufacturing process or raw materials used that could explain these events.

CSL has instead come to the preliminary conclusion that its vaccine manufacturing method retains more virus components than other manufacturers' methods, and the characteristics of the components used in 2010 triggered an excessive immune response in some young children.

The company is now experimenting with methods including increasing the amount of splitting agent used to decrease the amount of reactive virus components in Fluvax while still retaining its effectiveness in adults and older children.

CSL Biotherapies vice-president of medical and research, Dr Darryl Maher, said the company is confident it can strike the right balance.

“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,” he said.

Maher said the company will continue to support the age restrictions on Fluvax until its manufacturing process is shown to consistently produce a safe and effective vaccine for young children.

CSL (ASX:CSL) shares fell 1.22 per cent on Wednesday, the day the preliminary conclusion was announced, and were trading unchanged as of 10am on Thursday.