Jun 20, 2012 (CIDRAP News) – Australia's CSL Biotherapies said today that viral components of its Fluvax seasonal flu vaccine led to the unexpected rise in febrile seizures in young Australian children during the 2010 flu season.
The company, based in Parkville, Victoria, released preliminary findings from its 2-year investigation at an immunization conference today in Darwin, according to a CSL press release. The investigation was monitored by Australia's Therapeutic Goods Administration and the US Food and Drug Administration.
The study compared febrile seizure rates in children who received Fluvax compared with those who received another licensed flu vaccine. Fluvax had not been linked to febrile seizures before 2010, but the rate of the adverse event that year was estimated to be 5 to 7 per 1,000 doses in children younger than 5.
After an extensive review of all manufacturing aspects, CSL investigators concluded that its manufacturing process retains more virus component than that of other manufacturers. They also determined that the particular characteristics of 2010 virus components elicited an excessive immune response in some young children, which can trigger fever and febrile convulsions.
Darryl Maher, MBBS, PhD, the company's vice president of medical and research, said, "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."
CSL said its experiments have found that increasing the amount of splitting agent can reduce the amount of reactive virus components in Fluvax. It is conducting more studies to determine how Fluvax's reactive virus components contributed to the events in children and if modifications can be made to reduce them.
Fluvax is not licensed for children younger than age 5 and is currently recommended only for children from 5 to 9 years old if no other licensed flu vaccine is available. An Australian Technical Advisory Group on Immunization review recently found that Fluvax still has an acceptable safety profile in people age 10 and older.
Jun 20 CSL statement