Australian biotech company CSL has wrapped up a four-year investigation into why some children who received its flu vaccine in 2010 had febrile seizures. Studies found strains in that year’s Fluvax vaccine overstimulated the immune system of some children and adding more virus-splitting agent could reduce that response.

During the 2010 flu season in the Southern Hemisphere, statistics show for every 1,000 doses administered about five to seven children under age five experienced adverse reactions, including fever and convulsions. CSL removed the vaccine from the market.

The company then started a complex investigation with help from researchers all over the world; it included more than 200 lab experiments. There was oversight from Australia’s Therapeutic Goods Administration and the U.S. Food and Drug Administration. 

The studies show CSL’s manufacturing process retained more virus component than that of other manufacturers. The vaccine contained an influenza B component and the 2009 H1N1 virus component. Researchers reported that combination elicited heightened cytokine and immune response in some children, which may have been associated with the febrile seizures.

The studies also found that increasing the level of splitting agent used during manufacturing would help reduce the inflammatory response and, in turn, decrease the seizure risk.

As a result of this investigation, CSL has changed its manufacturing process of Fluvax by adding more virus-splitting agent. Clinical trials show this modification doesn’t decrease the vaccine’s effectiveness.

CSL still recommends Fluvax not be used in children under age five until more clinical trials are conducted.

News, Vaccine Injury News Studies Reveal What Caused Seizures in Children who Received Flu Vaccine