The flu shot carries a tiny risk of developing a debilitating neurological disorder, Toronto researchers say, but they warn that the risk of dying from influenza are much higher.

The vaccine has been controversial since the swine flu scare of 1976, when out of millions who were vaccinated, a handful of Americans developed Guillain-Barré syndrome, a paralysing condition that mimics polio.

In most cases, GBS reverses itself within a few months, but it may cause permanent damage.

Although suspicions of a link between the flu vaccine and GBS have lingered for 30 years, it has been difficult for researchers to show a cause-and-effect relationship, since the vaccine isn't the only trigger.

To look for one, Dr. David Juurlink of the Institute for Clinical Evaluative Sciences at the University of Toronto and his team studied people in Ontario, which launched a program for universal flu shots in 2000. 

In Monday's issue of the Archives of Internal Medicine, the researchers compared the number of hospitalizations for GBS before and after the immunization program, concluding there was no significant difference.

GBS risk tiny compared to flu

The risk exists, but it is on the order of being hit by lightning, while the benefits of vaccination are substantial, Juurlink said.

In an average year, one in six Canadians gets the flu. At the population level, the risk of dying of the flu is 1.3 in 10,000, with most deaths among the elderly.

According to Juurlink's study, the risk of getting GBS from a flu shot is one or two in a million. That translates into a 70-times-greater chance of dying from the flu, than getting the neurological disorder from a flu shot.

Each year, between 500 and 1,500 Canadians — mostly the elderly and young children — die annually from flu complications.

But some argue public health officials already overstate the benefits of the vaccine, especially for young healthy adults, said Dr. Lisa Schwartz of Dartmouth Medical School in Hanover, N.H. 

"For younger people less than 65, the benefit is really in terms of decreased days of being sick, and again, the benefit of the vaccine is not vast," said Schwartz.

The study isn't likely to change the mind of Winnipeg resident Percy Hannesson, who developed GBS after a flu shot 13 years ago and now avoids the vaccine, along with the rest of his family.

Hannesson was in the hospital for about two years. When he came home, he was unable to feed himself because of damage to the nerves in his hands. He also couldn't downhill ski or travel.

Hannesson said he doesn't tell others what to do about the flu shot, leaving it up to them.

Most Canadians are only now receiving flu shots because a manufacturing problem delayed delivery of the vaccine.

Juurlink's team concluded that people who receive flu shots should be told about the risk for GBS, and a surveillance plan should be included in mass vaccination programs.

The study's findings do not change the risk-benefit for anyone, said Dr. Allison McGeer, a longtime advocate of flu shots for the young and old. McGeer also worked on the study.