* Rise in fever-related seizures reported after Fluzone
* FDA: Data are preliminary, investigation ongoing
* Sanofi shares down 0.5 percent on NYSE
* No children had long-term effects (Adds Sanofi, FDA comments, share movement, byline)
By Lisa Richwine
WASHINGTON, Jan 20 (Reuters) - U.S. health officials are investigating a rise in reports of a type of seizure following vaccination with a Sanofi-Aventis SA <SASY.PA> flu vaccine, the Food and Drug Administration said on Thursday.
The febrile seizures, or seizures related to a fever, have primarily been reported in children younger than 2, the FDA said in a statement on its website.
Data are preliminary and the FDA and Centers for Disease Control and Prevention are investigating if the seizures are associated with the vaccine, called Fluzone, or if other factors were involved, the FDA said.
Having a fever can cause a seizure in some children. About 4 percent of young children will have at least one febrile seizure in their lifetimes, the FDA said.
"In the cases reported, all children recovered and no lasting effects have been seen," the FDA said.
The CDC recommends everyone older than 6 months get a flu vaccine annually. That recommendation has not changed, the FDA said.
The Sanofi-Aventis flu shot is the only one recommended for infants and children ages 6 months to 23 months during the current flu season.
The company said it was working with the FDA to investigate the cases.
"At this point no correlation between influenza vaccine and febrile seizures has been established. Adverse events after vaccination may be causally related to vaccine or may be coincidental," Sanofi-Aventis said in a written statement.
The risk of severe illness from influenza is higher among young children, especially under age 2. About 9 out of 10,000 children ages 6 months to 23 months land in the hospital each season for flu-related problems, the FDA said.
Shares of the French drugmaker were down 0.5 percent at ${esc.dollar}33.93 in early afternoon trading on the New York Stock Exchange.
The FDA posted the notice at http://link.reuters.com/cep47r. (Reporting by Lisa Richwine; editing by Andre Grenon, Dave Zimmerman)
Our Standards: The Thomson Reuters Trust Principles.
