Possible link between Pandemrix swine flu vaccine and narcolepsy

Research published in the BMJ yesterday suggests a possible link between the swine flu vaccine given to children in the UK and Europe during the epidemic in 2009 and 2010 and a rare condition called narcolepsy, which causes people to fall asleep suddenly without any warning and at any time of the day.

The BMJ paper studied 75 English children aged 4 to 18 years with narcolepsy, and found that 11 of these children had received the Pandemrix vaccine during the 14 months before their symptoms began. These figures suggest that the vaccine leads to an increased risk of developing narcolepsy, a finding that echoes that of studies in Finland and Sweden.

In total, around 668,000 UK children in this age group received the vaccine, and 11 were subsequently diagnosed with narcolepsy. The researchers calculate that this means one additional child aged 4 to 18 years developed narcolepsy for every 52,000 to 57,000 immunised with Pandemrix. No increased risk has been found outside of this age range.

The nature of flu pandemics, in which a new strain of virus crosses from animals into humans and spreads extremely rapidly, means that the implementation of the vaccination programme, including development and trialling of the specific vaccine, has to happen very quickly. Clinical trials reveal any common side effects, but it stands to reason that a side effect that affects just 1 in 50,000 people will not become clear during the trials stage, when the vaccine is given to several thousand people. This is why the ongoing monitoring of all drugs, including vaccines, is so important. The fact that this possible link has been picked up and can be investigated shows the effectiveness of the monitoring system. Lessons learned during this time can be used to further improve the planning and monitoring of future immunisation programmes during pandemics.

This study does not prove that there is a causal link between the vaccine and narcolepsy, although the data is statistically significant, meaning it is unlikely to have arisen by chance. Narcolepsy is a disease that often goes undiagnosed for many years. It is possible that the vaccine does not cause the condition, but merely accelerates its onset, making it easier and quicker to diagnose. If this is the case, we would expect there to be a reduction in newly diagnosed cases in subsequent years. Follow-up studies in Finland and Ireland, where vaccine coverage was high and where we would expect a marked reduction in diagnoses in years to come, will show whether or not this is the case.

Although this vaccine retains its EU licence, it is unlikely that it would be used again in future due to the specific nature of flu epidemics. However, this study does have implications for the future use of other pandemic flu vaccines, in particular those containing the adjuvant AS03. An adjuvant is a substance that improves the effectiveness of a vaccine. AS03 (which stands for adjuvant system 03) is a relatively new adjuvant made by GlaxoSmithKline. It is not used in any vaccines currently used in the routine schedule in the UK. It is used in another pandemic flu vaccine called Arepanrix which has been given to over two million children in Canada, without apparently causing any increase in the incidence of narcolepsy. The authors of the BMJ paper suggest that more studies are needed to assess what risks, if any, are associated with pandemic flu vaccines, to inform the use of such vaccines in the event of a future pandemic.

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