As an executive with a big Bay Street company, Brian Claman does not "have the time to waste being sick."

So, when flu shots were offered at the office a year ago, he was quick to head to the boardroom and get vaccinated.

"I've had the flu a couple of times and it's nasty, so I figured it was a win-win situation," Mr. Claman said.

Two weeks after his flu shot, Mr. Claman awoke with a pounding headache and a strange feeling in his feet. The doctor was reassuring, telling the 47-year-old businessman that the symptoms were probably related to stress.

His condition deteriorated, so he made his way to a hospital emergency room. His body was gradually going numb.

Doctors immediately recognized the tell-tale signs of Guillain Barré syndrome, a baffling, potentially fatal condition that resembles polio.

By afternoon, Mr. Claman was completely paralyzed. He was placed in intensive care and put on a respirator.

He spent the next eight months in hospital and now, a year after his flu shot, is just beginning to walk unassisted again.

"It's been a harrowing experience," Mr. Claman said in an interview.

"Never in my wildest dreams -- or maybe I should say nightmares -- could I have imagined almost losing my life to the flu shot," According to Health Canada, there have been 37 cases of GBS since 1987 where a link to the flu vaccine is suspected. But it cautions that because reporting is not mandatory, the number of cases is probably underreported, and that because GBS occurs for a number of other reasons, it is often difficult to make a causal link.

The mundane medical term for what happened to Mr. Claman is "adverse reaction." That usually means a little fever and maybe some swelling at the injection site, but a small minority suffer severe reactions such as Guillain Barré syndrome, an inflammatory disorder of the peripheral nerves (those outside the brain and spinal cord).

While the exact cause is unknown, GBS appears to be an autoimmune disease in which the body's disease-fighting system mistakenly attacks the covering of the nerves. At least half the cases seem to be triggered by a microbial infection. Mr. Claman suffered a severe reaction; usually GBS will reverse itself within a few months.

The link to vaccines was first made in 1976, when hundreds of people in the United States developed Guillain Barré after getting the swine-flu vaccine. Mr. Claman's experience, getting sick suddenly two weeks after the shot, is typical.

Public-health officials are quick to point out that while GBS is a devastating condition, it is rare, and getting the flu is a far more dangerous prospect.

In a paper published in the Canada Communicable Disease Report, Philippe De Wals, an epidemiologist in the department of community health services at the University of Sherbrooke, calculated that for a person over the age of 65 (those at greatest risk from the flu) the risk of dying of GBS after a flu shot is about one in 10 million, while the risk of contracting influenza and dying if a person is not vaccinated is about one in 1,000. In other words, the fear of GBS should not dissuade people (seniors, at least) because the risk of dying from not getting the shot is 10,000 times greater.

Mr. Claman knows the math all too well, but said it is meaningless to someone in his position.

"The rareness of complications means nothing if you're the one suffering from the adverse reaction," he said. "It's like the lottery: The odds mean nothing because everyone thinks they're going to win. With the vaccine, it's the opposite: Nobody thinks this can happen to them."

Despite his experience, Mr. Claman is not opposed to the flu vaccine or the public-health campaigns urging everyone to get a shot. But he thinks the message is too sugarcoated.

"Let's talk about the real risks of influenza and the real risks of the flu shot and let people make an informed decision," he said. "But let's not pretend that because a flu shot is generally a good idea that nothing bad is ever going to happen." Mr. Claman said his biggest loss was personal -- staying in hospital and away from his family, in particular a teenage son. Being off work for months during the prime of his earning power also took a financial toll.