https://www.cdc.gov/vaccinesafety/concerns/history/narcolepsy-flu.html

An increased risk of narcolepsy was found following vaccination with Pandemrix, a monovalent 2009 H1N1 influenza vaccine that was used in several European countries during the H1N1 influenza pandemic. Narcolepsy is a chronic neurological disorder caused by the brain’s inability to regulate sleep-wake cycles normally. This risk was initially found in Finland, and then some other European countries also detected an association. Most recently, scientists at the United Kingdom’s (UK) Health Protection Agency (HPA) have found evidence of an association between Pandemrix and narcolepsy in children in England. The findings are consistent with studies from Finland and other countries.

Pandemrix is manufactured by GlaxoSmithKline in Europe and was specifically produced for pandemic 2009 H1N1 influenza. It was not used before 2009, and has not been used since the influenza pandemic season (2009-2010). It contains an oil-in-water emulsion adjuvant called ASO3. Adjuvants are substances added to a vaccine to increase the body’s immune response to that vaccine.

Pandemrix was not licensed for use in the United States.

In response to the events in Europe, CDC reviewed data from the U.S. Vaccine Adverse Event Reporting System (VAERS) and the Vaccine Safety Datalink (VSD) and found no indication of any association between U.S.-licensed H1N1 or seasonal influenza vaccine and narcolepsy.

In 2014, CDC published a study on the association between 2009 H1N1 influenza vaccines, 2010/2011 seasonal influenza vaccines, and narcolepsy. The analysis included more than 650,000 people who received the pandemic flu vaccine in 2009 and over 870,000 people who received the seasonal flu vaccine in 2010/2011. The study found that vaccination was not associated with an increased risk for narcolepsy.

CDC recommends influenza vaccination as the best way to protect from influenza disease and its complications. See CDC influenza vaccine recommendations.