H1N1 vaccine associated with small but significant risk of Guillain-Barre syndrome

July 10, 2012

Guillain-Barre syndrome (GBS) is usually characterized by rapidly developing motor weakness and areflexia (the absence of reflexes). "The disease is thought to be autoimmune and triggered by a stimulus of external origin. In 1976-1977, an unusually high rate of GBS was identified in the United States following the administration of inactivated 'swine' influenza A(H1N1) vaccines. In 2003, the Institute of Medicine (IOM) concluded that the evidence favored acceptance of a causal relationship between the 1976 swine influenza vaccines and GBS in adults. Studies of seasonal influenza vaccines administered in subsequent years have found small or no increased risk," according to background information in the article. "In a more recent assessment of epidemiologic studies on seasonal influenza vaccines, experimental studies in animals, and case reports in humans, the IOM Committee to Review Adverse Effects of Vaccines concluded that the evidence was inadequate to accept or reject a causal relationship."

Philippe De Wals, M.D., Ph.D., of Laval University, Quebec City, Canada and colleagues conducted a study to assess the risk of GBS following pandemic influenza vaccine administration. In fall 2009 in Quebec an immunization campaign was launched against the 2009 influenza A(H1N1) pandemic strain. By the end of the year, 4.4 million residents had been vaccinated. The study included follow-up over the 6-month period of October 2009 through March 2010 for suspected and confirmed GBS cases reported by physicians, mostly neurologists, during active surveillance or identified in the provincial hospital summary discharge database. Immunization status was verified.

Over the 6-month period, 83 confirmed GBS cases were identified. Twenty-five confirmed cases had been vaccinated against 2009 influenza A(H1N1) 8 or fewer weeks before disease onset, with most (19/25) vaccinated 4 or fewer weeks before onset. Analysis of data indicated a small but significant risk of GBS following influenza A(H1N1) vaccination. The number of cases attributable to vaccination was approximately 2 per 1 million doses. The excess risk was observed only in persons 50 years of age or older.

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

In an accompanying editorial, Mark C. Steinhoff, M.D., of the Cincinnati Children's Hospital Medical Center, and Noni E. MacDonald, M.D., M.Sc., F.R.C.P.C., of Dalhousie University, Halifax, Nova Scotia, Canada, write that "taken together, these studies partially assuage concerns about safety of adjuvanted pandemic during pregnancy."

"However, more studies are needed examining other types of vaccine adjuvants. In addition, observational studies of vaccines are limited by biases, including selection bias, as well as confounding by indication. Thus, future studies with improved statistical designs including prospective follow-up studies using virological end points with adjustments for selection, seasonality, and other biases are needed to confirm these data."

Explore further: No substantial link between swine flu vaccine and Guillain-Barre syndrome, confirm experts

More information: JAMA. 2012;308[2]:175-181.
JAMA. 2012;308[2]:184-185.

Related Stories

No substantial link between swine flu vaccine and Guillain-Barre syndrome, confirm experts

July 13, 2011
Adjuvanted vaccines used during the 2009 swine flu pandemic did not increase the risk of Guillain-Barré syndrome substantially, if at all, finds a large Europe-wide study published in the British Medical Journal today. ...

Scientists examine risk of poor birth outcomes following H1N1 vaccination

July 10, 2012
In studies examining the risk of adverse outcomes after receipt of the influenza A(H1N1) vaccine, infants exposed to the vaccine in utero did not have a significantly increased risk of major birth defects, preterm birth, ...

Recommended for you

Google searches can be used to track dengue in underdeveloped countries

July 20, 2017
An analytical tool that combines Google search data with government-provided clinical data can quickly and accurately track dengue fever in less-developed countries, according to new research published in PLOS Computational ...

MRSA emerged years before methicillin was even discovered

July 19, 2017
Methicillin resistant Staphylococcus aureus (MRSA) emerged long before the introduction of the antibiotic methicillin into clinical practice, according to a study published in the open access journal Genome Biology. It was ...

New test distinguishes Zika from similar viral infections

July 18, 2017
A new test is the best-to-date in differentiating Zika virus infections from infections caused by similar viruses. The antibody-based assay, developed by researchers at UC Berkeley and Humabs BioMed, a private biotechnology ...

'Superbugs' study reveals complex picture of E. coli bloodstream infections

July 18, 2017
The first large-scale genetic study of Escherichia coli (E. coli) cultured from patients with bloodstream infections in England showed that drug resistant 'superbugs' are not always out-competing other strains. Research by ...

Ebola virus can persist in monkeys that survived disease, even after symptoms disappear

July 17, 2017
Ebola virus infection can be detected in rhesus monkeys that survive the disease and no longer show symptoms, according to research published by Army scientists in today's online edition of the journal Nature Microbiology. ...

Mountain gorillas have herpes virus similar to that found in humans

July 13, 2017
Scientists from the University of California, Davis, have detected a herpes virus in wild mountain gorillas that is very similar to the Epstein-Barr virus in humans, according to a study published today in the journal Scientific ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.