WASHINGTON The flu vaccine can slightly raise the risk of a potentially disabling neurological disorder called Guillain-Barre syndrome, researchers said on Monday, but they stressed the vaccine's benefits far outweigh its risks.
Canadian researchers, writing in the journal Archives of Internal Medicine, estimated that one to two people per million who get the flu vaccine will develop Guillain-Barre syndrome as a result. The ailment normally affects about one of every 100,000 people per year.
The researchers estimated that getting the vaccine raises the already very small risk of developing Guillain-Barre syndrome by about 45 percent.
"The risk is infinitesimal," Dr. David Juurlink of the Institute for Clinical Evaluative Sciences at the University of Toronto, the lead researcher, said in an interview. "It's somewhere in the vicinity of being struck by lightning."
But Juurlink said Guillain-Barre syndrome was serious and people should be told of the risk before getting the vaccine.
"The risk is so small and the benefits are so substantial that I think no one should be dissuaded from getting a flu shot based upon these findings. I think basically it's a no-brainer in almost every circumstance," Juurlink added.
Juurlink said that immunizing a million people averted at least tens of thousands of cases of influenza and perhaps thousands of deaths.
Juurlink and his colleagues based their findings on a study of residents of the province Ontario, where a universal influenza immunization program was begun in 2000 offering free annual vaccinations to residents age 6 months and above.
The researchers said previous studies on a link between the flu vaccine and Guillain-Barre syndrome were inconclusive.
Guillain-Barre (pronounced ghee-yan bah-ray) syndrome is an inflammatory disorder of the peripheral nerves, or those outside the brain and spinal cord, characterized by rapid onset of weakness and often paralysis of the legs, arms, breathing muscles and face.
In the illness, which can be life-threatening, the body's immune system mistakenly attacks part of the nervous system. The exact cause remains elusive and there is no known cure although treatment can reduce its severity and speed recovery in most patients.
It came to public attention three decades ago when it struck a number of people who received the swine flu vaccine. The disease also is called acute inflammatory demyelinating polyneuropathy and Landry's ascending paralysis.