Abstract

CONTEXT
In fall 2009 in Quebec, Canada, an immunization campaign was launched against the 2009 influenza A(H1N1) pandemic strain, mostly using an AS03 adjuvant vaccine. By the end of the year, 57% of the 7.8 million residents had been vaccinated.
OBJECTIVE
To assess the risk of Guillain-Barré syndrome (GBS) following pandemic influenza vaccine administration.
DESIGN
Population-based cohort study with follow-up over the 6-month period October 2009 through March 2010. The investigation was ordered by the chief medical officer of health in accordance with the Quebec Public Health Act.
SETTING
All acute care hospitals and neurology clinics in Quebec.
POPULATION
Suspected and confirmed GBS cases reported by physicians, mostly neurologists, during active surveillance or identified in the provincial hospital summary discharge database. Medical records were reviewed and cases classified according to Brighton Collaboration definitions (categorized as level 1, 2, or 3, corresponding to criteria of decreasing certainty in diagnosis). Immunization status was verified and denominators were estimated from the provincial immunization registry (4.4 million vaccinated) and census data (total target population aged ≥6 months, 7.8 million), with a total of 3,623,046 person-years of observation.
MAIN OUTCOME MEASURES
Relative and attributable risks were calculated using a Poisson model and the self-controlled case-series method.
RESULTS
Over a 6-month period, 83 confirmed GBS cases were identified, including 71 Brighton level 1 through 3 cases. 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. In the Poisson model, the age- and sex-adjusted relative risk was 1.80 (95% CI, 1.12-2.87) for all confirmed cases during the 8-week postvaccination period and was 2.75 (95% CI, 1.63-4.62) during the 4-week postvaccination period. Using the self-controlled case-series method, relative risk estimates during the 4-week postvaccination period were 3.02 (95% CI, 1.64-5.56) for all confirmed cases (n = 42) and 2.33 (95% CI, 1.19-4.57) for Brighton level 1 through 3 cases (n = 36). The number of GBS cases attributable to vaccination was approximately 2 per 1 million doses. There was no indication of an excess risk in persons younger than 50 years.
CONCLUSIONS
In Quebec, the 2009 influenza A(H1N1) vaccine was associated with a small but significant risk of GBS. It is likely that the benefits of immunization outweigh the risks.

Links

Publisher Full Text

Authors

De Wals P, Deceuninck G, Toth E, Boulianne N, Brunet D, Boucher RM, Landry M, De Serres G

Institution

Department of Social and Preventive Medicine, Laval University, Quebec City, Quebec, Canada. Philippe.De.Wals@ssss.gouv.qc.ca

Source

JAMA : the journal of the American Medical Association 308:2 2012 Jul 11 pg 175-81

MeSH

Adjuvants, Immunologic
Adolescent
Adult
Aged
Child
Child, Preschool
Female
Guillain-Barre Syndrome
Humans
Immunization Programs
Infant
Influenza A Virus, H1N1 Subtype
Influenza Vaccines
Influenza, Human
Male
Middle Aged
Population Surveillance
Quebec
Risk
Time Factors
Vaccination
Young Adult

Pub Type(s)

Journal Article
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

22782419