Probe on narcolepsy-H1N1 vaccine link finds genetic risk factor

Sep 1, 2011 (CIDRAP News) – A final report from Finnish health officials on the link between the 2009 H1N1 Pandemrix vaccine and narcolepsy confirmed the link, finding a greater risk than their earlier estimate and identifying a genetic risk factor in all patients.

In a statement on the findings today, a task force from Finland's National Institute for Health and Welfare also said an immunologic study found that one quarter of those who experienced narcolepsy after vaccination had antibodies that bound to the AS03 adjuvant component of the Pandemrix vaccine, which they said is a preliminary finding that requires more investigation.

Today's report put the increased risk of narcolepsy with vaccination at 6 cases per 100,000 people, which amounts to a 12.7-fold greater risk than in those who had not been vaccinated. The task force's first estimate in a January preliminary report was a nine times greater risk.

Some countries, mostly Nordic, have reported a link between the vaccine and narcolepsy in young people. Pandemrix, made by GlaxoSmithKline (GSK), is one of the 2009 H1N1 vaccines used in Europe during the pandemic.

In July the European Medicines Agency (EMA), in issuing its final review on the link, recommended a labeling change that limits the vaccine's use to protecting children and teens from the 2009 H1N1 virus when seasonal flu vaccine isn't available.

Finnish officials haven't found an increased risk in children younger than 4 or among adults older than 19.

In reporting the genetic findings in vaccinated patients who had narcolepsy, the task force said the risk factor for the condition is strongly linked to genetic factors that regulate immune responses. "Narcolepsy is considered an immune-mediated disease," they wrote.

Antibody tests found that less than 10% of those who had narcolepsy had been infected with the 2009 H1N1 virus, which led the group to conclude that infection with the strain doesn't appear play a significant role or show a combined effect with Pandemrix vaccination and narcolepsy onset.

The task force said so far Finland and Sweden are the only countries that have confirmed the link between Pandemrix and narcolepsy, though Norway and France have reported higher-than-expected numbers of cases. It added that several studies on the link are under way in countries that used considerable amounts of Pandemrix and Arepanrix, another GSK pandemic vaccine made in Canada that included the same adjuvant.

As of Aug 25, Finnish health officials had received reports of 98 narcolepsy cases in people who had been vaccinated with Pandemrix, and 79 were in patients between ages 4 and 19 years old. The condition was associated with cataplexy, a sudden and transient loss of muscle tone, in 78 cases.

Despite the limited number of unexpected and unfortunate narcolepsy cases, Finnish officials said the overall benefits of the vaccine still outweigh the risks.

They added that research teams in Finland and other countries are exploring the immunogenetics, pathogenesis, and clinical course of narcolepsy.

GSK spokeswoman Jennifer Armstrong told CIDRAP News that the Finnish data are similar to what officials reported earlier this year. She said Glaxo is committed to patient safety and is working closely with the EMA and other regulatory groups.

"Further information from ongoing studies is still needed in order to gain additional insight into the cause of the reported cases of narcolepsy," Armstrong said. "In addition, GSK has committed to conduct further research into any potential association between Pandemrix and narcolepsy and will seek independent expert advice on this research activity, as agreed with the EMA."

See also:

Sep 1 National Institute for Health and Welfare press release

Feb 1 CIDRAP News story "Finland finds link between vaccine and narcolepsy cases"

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