TUESDAY, Feb. 26, 2013 (HealthDay News) -- A British study finds that children and teens who were vaccinated during the 2009 swine flu outbreak are at increased risk for narcolepsy, a disorder that causes people to fall asleep during the day.
The particular flu vaccine involved has never been licensed for use in the United States, according a statement on the U.S. Centers for Disease Control and Prevention website.
Researchers looked at data from children and teens aged 4 to 18 who were treated at sleep centers and neurology centers in England, and concluded that receiving the Pandemrix vaccine was associated with a 14- to 16-fold increased risk of developing narcolepsy.
They also determined that one in 52,000 to 57,500 doses of the vaccine are associated with narcolepsy, according to the study published online Feb. 26 in the journal BMJ.
The findings are consistent with previous studies in other countries, said Elizabeth Miller, of the Health Protection Agency in the United Kingdom, and colleagues. For example, a 2012 study from Finland found a 13-fold increased risk of narcolepsy in children and teens aged 4 to 19 who received the Pandemrix vaccine.
The authors of the new study wrote that the findings do indicate a "causal" link between the vaccine and the sleep disorder. They added, however, that the risk may still be overestimated and added that long-term monitoring of children and teens who received the vaccine is needed to determine the exact level of risk.
The 2009 H1N1 swine flu pandemic sickened millions of people and caused more than 18,000 deaths in more than 200 countries. In England, the Pandemrix vaccine was introduced in October 2009. By March 2010, 24 percent of healthy children younger than age 5 and 37 percent of those aged 2 to 15 in an at-risk group had been vaccinated.
The U.S. National Institute of Neurological Disorders and Stroke has more about narcolepsy.