Children are 4-9 times as likely to develop narcolepsy if they were vaccinated with Pandemrix during the outbreak of the H1N1 swine flu in 2009.
This was one of the findings presented by scientists from Finland, Norway and Sweden at a recent vaccine conference organised by the Danish National Institute for Health Data and Disease Control (SSI).
The surprising link between Pandemrix and narcolepsy was discovered by chance when Finnish sleep researchers recently started reporting about increased instances of the disorder.
In Finland and Sweden, an abrupt increase in narcolepsy cases was observed after the flu pandemic in 2009-2010. In Finland, 121 cases of this otherwise extremely rare disorder were registered, while Sweden had 168 such cases, 150 of which were below the age of 18.
Scientists have yet to find a biological explanation for this link, but some have suggested that people with a specific type of genes are particularly susceptible to the disorder.
“Our hypothesis is that Pandemrix doesn’t directly cause narcolepsy; rather, it triggers the disorder in people who are predisposed to it,” says Thyra Grove Krause, a consultant at the SSI.
Pandemrix has also been used in other countries, including Canada, where no increase in narcolepsy instances has been registered.
It is, however, a disorder that’s difficult to diagnose, and it can take a long time before the first symptoms are detected until a firm diagnosis is in place, explains Krause.
The main suspect in Pandemrix is AS03, a so-called adjuvant system, which is an agent added to a vaccine to boost its efficiency.
AS03 contains squalene, which is extracted from shark liver oil. The researchers suggest that this may be the substance that triggers narcolepsy, although this remains inconclusive.
The researchers have isolated two types of genes that are common in children who developed narcolepsy after being vaccinated with Pandemrix.
The two types are called HLA DQB1 *0602 and HLA (DR4)-DQA1*030.
If you have been vaccinated against the H1N1 virus, there’s still little need to worry about developing narcolepsy:
“Narcolepsy is a serious condition, but it’s also very rare – under normal circumstances it only affects one in 100,000 people,” says Krause.