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The question: I read a recent news story that said the vaccine used a few years ago to protect against the H1N1 flu virus could have caused narcolepsy in children. Should I be worried about having my children vaccinated this year? Is the flu shot safe?
The answer: It’s true researchers are investigating the possibility that the H1N1 flu shot, or the virus itself, may be linked to an apparent spike in cases of the sleep disorder.
However, you can rest assured that this year’s flu vaccine is very different from the one used to guard against H1N1 in 2009.
“H1N1 was a very special case – it was not the regular flu vaccine,” says Dr. Brian Murray, a sleep specialist at Sunnybrook Health Sciences Centre.
At the time, you may recall influenza experts were concerned the H1N1 virus –commonly known as the swine flu – could lead to an extremely deadly global pandemic. Pharmaceutical companies rushed special vaccines into production to deal with the potential threat.
Like regular seasonal flu shots, the H1N1 vaccines contained antigens, or proteins, that trigger the immune system to produce antibodies to fight the virus. But some of the H1N1 vaccines also included an adjuvant – or booster – to increase the body’s immune response. Using an adjuvant meant the vaccine could be made with fewer antigens. This helped speed up production of the pandemic flu shots, which were in great demand from governments around the world.
About a year later, doctors in Finland were among the first to report an unusual blip in narcolepsy cases especially among children and teens. Only one type of H1N1 vaccine had been used in Finland – Pandemrix which contained an adjuvant. In other countries where adjuvants were used – notably in Europe and China – doctors began to make similar observations.
Still, the actual number of cases remains relatively small compared to the millions of people who received the vaccine worldwide.
According to a report from the National Institute for Health and Welfare of Finland, the increased risk corresponds to about 6 extra cases of narcolepsy per 100,000 children vaccinated and one extra case per 100,000 adults who got the shot.
Narcolepsy is a rather uncommon neurodegenerative condition. It normally occurs among 25 to 50 out of every 100,000 people in the general population and rarely affects children.
Patients suffer from profound daytime drowsiness says Dr. Murray who is also an associate professor at the University of Toronto.
They can also experience a related problem called cataplexy – the sudden loss of muscle tone, particularly with an emotional trigger. “If you tell them a joke, they can fall down,” says Dr. Murray. “It sounds very bizarre, but there are pathways in the brain that suggest why that happens.”
Narcolepsy results from the loss of a brain chemical called orexin (also known as hypocretin) that plays a key role in regulating sleep-wake cycles.
Dr. Murray points out that the human mind typically exists in three different states – awake, REM sleep and slow-wave sleep.
“Orexin is a kind of psychic glue that holds you in one state or another and it is when you start to drift in between states there is a problem,” he explains. “You start to fall asleep while you are awake. Or, you lose muscle tone which is a normal feature of REM sleep, but it is abnormal for the waking state.”
Dr. Murray says it’s possible a component of the H1N1 vaccine leads the immune system to destroy orexin-producing cells in some people who are genetically predisposed to the disorder. But he cautioned a lot more work is needed to confirm such a theory.
The Brighton Collaboration, a vaccine-safety group sponsored by the World Health Organization and the U.S. Centers for Disease Control, is providing seed money to researchers who are investigating the matter.
With some of that funding Dr. Murray and Dr. Jeff Kwong, an epidemiologist with the Institute of Clinical Evaluative Sciences at Sunnybrook, are conducting a study to see if the vaccine is linked to a rise of narcolepsy cases in Ontario.
“It’s a gargantuan task,” says Dr. Murray. “We are trying to identify every patient who developed narcolepsy in Ontario, and then go through all the paper records of immunization status to figure out whether they got the vaccine or not.”
In Canada, the H1N1 vaccine was called Arepanrix. It was similar to Pandemrix used in Europe and included an adjuvant. (Some batches of non-adjuvanted vaccine were produced for pregnant women.)
The findings from the Ontario research, and other studies, could have important implications for the future use of adjuvants, said Dr. Murray.
For this flu season, though, adjuvants are not an issue. The vaccine doesn’t contain them. “Don’t let this prevent you from getting the regular flu vaccine,” says Dr. Murray. “This is not the same kind of scenario.”
Paul Taylor is Sunnybrook’s Patient Navigation Advisor. His column Personal Health Navigator provides advice and answers questions from patients and their families, relying heavily on medical and health experts. His blog is reprinted on healthydebate.ca with the kind permission of Sunnybrook Health Sciences Centre. Email your questions to AskPaul@sunnybrook.ca