27 February 2013
Health Protection Agency (HPA) scientists have found evidence of an association between Pandemrix flu vaccination and narcolepsy in children in England, according to the findings of a study published in the British Medical Journal. These findings are consistent with previous studies from Finland and Sweden which identified a similar association.
In collaboration with researchers from Papworth and Addenbrooke’s hospitals in Cambridge, the study looked at 75 children aged between four and 18 who were diagnosed with narcolepsy from January 2008 and who attended sleep centres across England. Eleven of these children had been vaccinated with Pandemrix before their symptoms began, seven of these within six months. This suggests a risk of narcolepsy following vaccination with Pandemrix of around one in every 55,000 doses of the vaccine.
The Pandemrix vaccine was recommended for use in children at risk of serious complications from influenza during the pandemic flu outbreak in 2009/10. It was also used occasionally in children during the 2010/11 flu season. Since July 2011 the use of Pandemrix in people under the age of 20 across Europe has been restricted.
Although prior to this study, there was no evidence to suggest an association in the UK, on the basis of the findings from Finland the HPA launched an in depth study in February 2011 with narcolepsy experts across England. This investigated whether there was evidence of an association between narcolepsy and Pandemrix as used in the UK.
Lead author Professor Liz Miller, a consultant epidemiologist with the HPA, said: "These findings suggest there is an increased risk in children of narcolepsy after Pandemrix vaccination and this is consistent with findings from studies in other European countries. However, this risk may be overestimated by more rapid referral of vaccinated cases. Long term follow up of people exposed to Pandemrix is needed before we can fully establish the extent of the association.
“Our findings have implications for the future licensing and use of adjuvanted pandemic vaccines. Further studies to assess the possible risk associated with other vaccines used in the pandemic, including those with and without adjuvants, are also needed to inform the use of such vaccines in the event of a future pandemic.”
Study co-author Dr John Shneerson, consultant physician from the Respiratory Support and Sleep Centre at Papworth Hospital in Cambridge, said: “Narcolepsy is thought to be due to a loss of function of a small group of cells in one of the sleep centres in the brain, as a result of an abnormal reaction of the body’s immune system. Pandemrix may have triggered an immune reaction against the sleep centre cells in those children who were genetically predisposed to develop narcolepsy. This study has been important in helping to shed light on the mechanism of how narcolepsy can develop.”
Narcolepsy is a chronic neurological disorder caused by the brain's inability to control sleep, particularly REM (dream) sleep. It leads to excessive daytime sleepiness usually accompanied by sudden episodes of muscle weakness triggered by strong emotions such as laughter – this is known as cataplexy. Narcolepsy has a genetic component but this has to be triggered by other factors in order for the condition to appear. 20,000 people in the UK are through to have narcolepsy - drug treatment and lifestyle measures are usually effective in relieving the symptoms.
Last reviewed: 26 February 2013