GlaxoSmithKline's Pandemrix swine flu vaccine has been linked
to cases of the rare sleep disorder narcolepsy in children in a scientific study
in England that confirms similar findings elsewhere in Europe.
The vaccine, more than 30 million doses of which were given
during the H1N1 flu pandemic in 2009-2010, contains a booster, or adjuvant, and
may have triggered an adverse immune reaction in some children at higher genetic
risk of narcolepsy, scientists said in new research published on
Researchers at Britain's Health Protection Agency (HPA) who
published the study in the British Medical Journal said the at least 14-fold
increased risk they found had "implications for the future licensing and use of
adjuvanted pandemic vaccines".
800 cases linked to the shot
Narcolepsy is a life-long disorder and thought to be an
auto-immune disease, in which a patient's immune system attacks the body's own
cells. Its symptoms include frequent bouts of daytime sleepiness and in its
severe forms it also causes night terrors, hallucinations and cataplexies - when
strong emotions trigger a sudden loss of muscle strength.
Studies in Finland, Sweden and Ireland have also found a
Pandemrix link to narcolepsy, and GSK says more than 800 cases linked to the
shot have been reported in Europe.
A spokesman for the British drug maker said: "We really want to
get to the bottom of this and understand more about the potential role of
Pandemrix in the development of narcolepsy.
"He added, however, that GSK believes "the available data are
insufficient to assess the likelihood of a causal association between Pandemrix
As reported earlier this month, scientists investigating the
link further are homing in on the vaccine's adjuvant, a booster called AS03, and
analysing whether its super-charging effect may have played a role.
According to the UK results, vaccination with Pandemrix at any
time was associated with a 14-fold increased risk of narcolepsy, whereas
vaccination within six months before onset of the disease was associated with a
16-fold increased risk.
"The increased risk of narcolepsy indicates a causal
association," said the research team led by Liz Miller, a consultant
epidemiologist with the HPA.
They added, however, that because of variable delay in
diagnosis, the risk may be overestimated because vaccinated children may have
been referred to specialist sleep clinics more rapidly.
Scientists said the risk translated into around one in 50 000,
lower than studies have found in other countries such as Finland and Sweden
where Pandemrix was used more widely and the risk was around one in 16 000 to 17
000 children vaccinated.
No cure but can be treated
In total, more than 30 million doses of the GSK shot were given
in 47 mainly European countries during the H1N1 flu pandemic.
It was not used in the United States.
The UK study looked at 75 children aged between four and 18 who
were diagnosed with narcolepsy from January 2008 and who attended sleep centres
Eleven of the children had been vaccinated with Pandemrix
before their symptoms began.
Finn stressed that Pandemrix is the only vaccine linked to this
problem: "There is nothing to suggest that it occurs after other flu vaccines or
vaccines against other diseases."
Narcolepsy is thought to be due to loss of function in cells
called hypocretin cells in one of the brain's sleep centres.
John Shneerson, a consultant physician from the Respiratory
Support and Sleep Centre at Papworth Hospital in Cambridge who co-led the UK
study, said Pandemrix may have triggered an immune reaction against those cells,
causing narcolepsy in some children who were genetically vulnerable.
Experts say around 25% of Europeans have a genetic profile
making them more susceptible. Narcolepsy has no known cure, but specialist
doctors say symptoms can be treated with drug combinations aimed at
re-regulating the sleep-wake cycle.