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Abstract
Objective: To assess the occurrence of narcolepsy after influenza vaccines used in the United States that contained the influenza A(H1N1)pdm09 virus strain.
Methods: A population-based cohort study in the Vaccine Safety Datalink with an annual population of more than 8.5 million people. All persons younger than 30 years who received a 2009 pandemic or a 2010–2011 seasonal influenza vaccine were identified. Their medical visit history was searched for a first-ever occurrence of an ICD-9 narcolepsy diagnosis code through the end of 2011. Chart review was done to confirm the diagnosis and determine the date of symptom onset. Cases were patients who met the International Classification of Sleep Disorders, 2nd edition, narcolepsy diagnostic criteria. We compared the observed number of cases after vaccination to the number expected to occur by chance alone.
Results: The number vaccinated with 2009 pandemic vaccine was 650,995 and with 2010–2011 seasonal vaccine was 870,530. Among these patients, 70 had a first-ever narcolepsy diagnosis code after vaccination, of which 16 had a chart-confirmed incident diagnosis of narcolepsy. None had their symptom onset during the 180 days after receipt of a 2009 pandemic vaccine compared with 6.52 expected, and 2 had onset after a 2010–2011 seasonal vaccine compared with 8.83 expected.
Conclusions: Influenza vaccines containing the A(H1N1)pdm09 virus strain used in the United States were not associated with an increased risk of narcolepsy. Vaccination with the influenza A(H1N1)pdm09 vaccine viral antigens does not appear to be sufficient by itself to increase the incidence of narcolepsy in a population.
GLOSSARY
- GSK=
- GlaxoSmithKline Biologicals;
- ICD-9=
- International Classification of Diseases, ninth revision;
- LAIV=
- live attenuated influenza vaccine;
- MIV=
- monovalent inactivated vaccine;
- MLAIV=
- monovalent live attenuated influenza vaccine;
- PPV=
- positive predictive value;
- RR=
- relative risk;
- TIV=
- trivalent inactivated vaccine;
- US=
- United States;
- VSD=
- Vaccine Safety Datalink
Footnotes
Vaccine Safety Datalink coinvestigators are listed on the Neurology® Web site at www.neurology.org.
The findings and conclusions in this report are those of the authors and do not necessarily represent the official position of the Centers for Disease Control and Prevention.
Go to Neurology.org for full disclosures. Funding information and disclosures deemed relevant by the authors, if any, are provided at the end of the article.
Supplemental data at Neurology.org
- Received May 2, 2014.
- Accepted in final form August 11, 2014.
- © 2014 American Academy of Neurology
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