H1N1 Vaccine Linked to Nervous Disorder

Guillain-Barre syndrome risk detected with H1N1 vaccination in 1 of 500000 shots

(RxWiki News) One of the conditions known to be a risk following some flu vaccinations is the autoimmune disease Guillain-Barre syndrome.

A Canadian study found that the H1N1 vaccine appears to be linked to a slightly higher risk of developing Guillain-Barre, a disorder that can cause nerve inflammation, muscle weakness, tingling and paralysis, because the immune system attacks the nervous system.

"Consult your doctor if you're uncertain whether you should get the flu vaccine."

Philippe De Wals, MD, PhD, of Laval University in Quebec City, Canada, and colleagues investigated whether the H1N1 vaccination, in 2009, led to any cases of the syndrome. Researchers have continually monitored flu vaccines for links to Guillain-Barre for the past several decades.

The first major evidence about a possible link between Guillain-Barre syndrome and flu vaccines occurred following the 1976-1977 flu epidemic, during which a higher rate of Guillain-Barre was detected among those who received the vaccine.

A 2003 report, by the Institute of Medicine, determined that the flu vaccine did cause a small number of cases of Guillain-Barre syndrome. The risk was estimated at just under one case in every 100,000 vaccinations.

Since then, seasonal flu vaccines have had a very small or no greater risk of the syndrome, and the most recent evidence has led the Institute of Medicine to state that the seasonal flu vaccine cannot be determined to cause or not cause the disorder.

Dr. De Wals and colleagues conducted a 6-month follow-up from October, 2009 to March, 2010 for cases of Guillain-Barre syndrome and confirmed whether the individuals had received the H1N1 vaccine or not.

A total of 83 cases of the disorder were identified, and 25 of those people had received the H1N1 vaccine within eight weeks or less of the start of their symptoms. Most - 19 of the 25 - had symptoms within a month of vaccination.

The researchers calculated that a risk for Guillain-Barre syndrome did exist for the H1N1 vaccine at a rate of approximately 2 cases per 1 million doses of the vaccine, primarily among adults aged 50 and older.

When compared against the risks of getting the flu and the risk of death associated with the flu, the researchers concluded that the benefits of the H1N1 flu vaccine outweighed the risks of getting Guillain-Barre syndrome from the shot.

"In Quebec, the individual risk of hospitalization following a documented influenza AH1N1 infection was 1 per 2,500 and the risk of death was 1/73,000," the authors wrote. "The H1N1 vaccine was very effective in preventing infections and complications. It is likely that the benefits of immunization outweigh the risks."

The study was published July 10 in JAMA. The research was funded by the Ministere de la Sante et des Services sociaux du Quebec and by the Public Health Agency of Canada-Canadian Institutes for Health Research Influenza Research Network.

Dr. De Wals received research grants, honoraria and travel expenses from vaccine manufacturers, including GlaxoSmithKline, Novartis, Sanofi Pasteur, Merck, and Pfizer.

Two other authors, Nicole Boulianne, MSc, and Gaston De Serres, PhD, have also received research grants from Sanofi Pasteur and GlaxoSmithKline. No other authors reported any disclosures.

Review Date: 
July 8, 2012