Swine flu vaccine linked to increased risk of rare nerve disorder

The 2009 human "swine flu" vaccine given to millions of Canadians was associated with twice the normal risk of developing Guillain-Barre syndrome — a rare but potentially paralyzing nerve disorder, Quebec researchers are reporting.

With Guillain-Barre syndrome, or GBS, the immune system attacks the body's peripheral nerves, causing rapidly progressing muscle weakness and sometimes paralysis.

In a new study led by Quebec City's Laval University, researchers looked at all suspected and confirmed cases of GBS as reported by doctors — mostly neurologists — and hospital discharge records starting in the fall of 2009, when more than half of Quebec's population was vaccinated against H1N1 as part of mass immunization campaigns that rolled out nationwide. Quebec's chief medical officer of health ordered the investigation.

By the end of the year, 4.4 million Quebec residents had received the pandemic vaccine.

Over a six-month followup period between October 2009 and March 2010, 83 confirmed GBS cases were identified; 42 occurred in people who had been recently immunized.

Twenty-five developed symptoms within eight weeks of vaccination; of those, most — 19 — developed the syndrome within four weeks.

Overall, the Laval group calculates that the number of cases that can be attributed to the human swine flu shot was approximately two per one million doses.

The risk of contracting GBS from a normal seasonal flu shot has been estimated at about half that — an additional one case per million people vaccinated.

Despite the small but statistically significant increased risk — which was seen only in people aged 50 or older (GBS is more common in older adults) — the researchers believe the benefits of immunization likely outweigh the risks.

In Quebec, the risk of being hospitalized with H1N1 infection was one per 2,500; the risk of death was one per 73,000.

"The H1N1 vaccine was very effective in preventing infections and complications," the team writes in this week's edition of the Journal of the American Medical Association.

"The risk (of GBS) is of low magnitude — and it's probably much lower than the benefit of vaccination in case of a pandemic," said lead author Dr. Philippe De Wals, a professor in the department of social and preventive medicine at Laval. Most people recover from GBS, he added.

In 1976, when swine flu was found in soldiers at Fort Dix, N.J., the U.S. government launched a mass vaccination of more than 40 million people against a pandemic that never happened. The shots were halted after 10 weeks, after an unusually higher cluster of GBS was discovered during active surveillance for reactions to the shots.

According to World Health Organization experts, for no clear biological explanation, the shots increased the risk of GBS in adults within the first six weeks following vaccination.

As Canada embarked on the largest vaccination program in the nation's history, doctors and health officials were urged to check for GBS and other potential adverse events.

In a related paper, a nationwide study in Denmark involving more than 53,000 infants — nearly 7,000 of whom were exposed to H1N1 vaccine in the womb — found no significant increased risk of major birth defects, preterm birth or fetal growth restriction in babies born to women who were vaccinated against H1N1 during pregnancy.

"Pregnant women were among the main target groups prioritized for vaccination (against the pandemic strain), and an estimated 2.4 million women were vaccinated during pregnancy in the United States alone," the team, from the Statens Serum Institut in Copenhagen, writes.

In Canada, public health officials recommended pregnant women be among the first to be vaccinated when the H1N1 vaccine became available. But the rapid development of the vaccine, as well as the push to get it out ahead of a second wave of infection, raised concerns about safety, particularly among expectant mothers.

In an accompanying editorial, Dr. Noni MacDonald, of Dalhousie University, and co-author Mark Steinhoff of the Cincinnati Children's Hospital Medical Center, said that the studies, taken together, should help somewhat alleviate concerns about the safety of pandemic flu shots in pregnancy.

www.vancouversun.com/health/Swine+vaccine+linked+increased+risk+rare+nerve+disorder/6912656/story.html