Convulsions in children immunized with a CSL Ltd. flu shot probably were caused by an excessive immune response to viral components in the vaccine, according to preliminary findings of a two-year study.
Use in children younger than 6 years of CSL’s Fluvax vaccine, to protect against the three main influenza strains circulating in the 2010 Southern Hemisphere winter, was suspended by Australian health officials in April of that year. Doctors reported a nine-fold increase in fever and convulsions in children following immunization with Fluvax.
CSL, the Southern Hemisphere’s only flu-vaccine maker, hasn’t been able to license Fluvax for use in young children since the complications were noted. An investigation into the cause indicated CSL’s manufacturing method preserves more short-gene fragments and lipids from the virus than other makers, the Melbourne-based company said today.
“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,” Darryl Maher, vice president of medical and research at CSL’s biotherapies division, said in a statement.
CSL declined 1.2 percent to A$38.85 at the close of trading on the Australian stock exchange, paring to 21 percent the stock’s gain this year.
The findings were drawn from an investigation monitored by Australia’s drugs regulator. Results of the investigation were presented at an immunization meeting in Darwin today.
Fever-induced seizures in children vaccinated with Fluvax were observed at a rate of five to seven cases of per 1,000 doses, compared with an incidence of febrile convulsions of 0.08 to 0.17 with other flu vaccines, Australia’s Therapeutic Goods Administration said in a 2010 report.
Vaccination with Fluvax vaccine in 2010 may have caused two to three hospital admissions for febrile convulsions for every flu-related admission it prevented, doctors from Melbourne and Perth wrote in a 2010 study.
Particular characteristics of gene fragments or lipids from two of the flu strains used in the 2010 Fluvax may have led it to being more reactive in some young children compared with CSL vaccines used in previous seasons, the company said today. Inactivated whole virus and clusters of pieces of virus split by a chemical process may have contributed, and are under investigation.
Fluvax isn’t licensed in Australia for use in children under 5 years and is only recommended for at-risk children ages 5 to 9 years if no other licensed influenza vaccine is available.
CSL is working to better understand the cause of the adverse events and identify potential manufacturing-process changes that will prevent them from happening again, it said.
“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,” Maher said.