Sep 21, 2012 (CIDRAP News) – French researchers have found a significant link between one 2009 H1N1 vaccine and narcolepsy in adults, a finding that is likely to prompt some countries to take a fresh look to see if adult cases have surfaced in the wake of pandemic vaccine campaigns.

The French findings are part of a larger investigation under way through the Vaccine Adverse Event Surveillance and Communication (VAESCO) Consortiu led and funded by the European Centre for Disease Prevention and Control (ECDC). The data are from a case-control study that was partially included yesterday in a detailed technical report from the ECDC that explored the vaccine-narcolepsy link in eight European countries, including some that didn't report the problem.

Full findings from the French case-control study appeared yesterday on the Web site of the French Agency for the Safety of Medicines and Health Products (ANSM), a group that is similar to the US Food and Drug Administration.

Only one vaccine has been linked to the narcolepsy cases, Pandemrix, a GlaxoSmithKline (GSK) product that contains its AS03 adjuvant. The vaccine was not used in the United States during the 2009 H1N1 vaccine campaign, but several European countries used it alone or alongside other vaccine formulations. Canada and Brazil also used a very similar GSK pandemic vaccine containing the AS03 adjuvant.

Yesterday's ECDC report confirmed the link between narcolepsy and pandemic 2009 vaccination in Finnish and Swedish kids, and reported that a sensitivity analysis found a narcolepsy link to vaccinated adults when data were pooled from countries that hadn't already noted an association.

The ECDC said more data and case reports will be needed to better understand the link between narcolepsy and the vaccine.

The French researchers used a study protocol that was developed by VAESCO for use in the larger ECDC investigation. However, they noted that the study periods used by the wider study and the analysis specific to France are different, with the French study period starting 6 months later and ending 10 months later.

In the report yesterday, French investigators said 51 cases of narcolepsy were reported in French patients who were immunized against the pandemic virus; 47 received Pandemrix, but only 3 received Panenza (a nonadjuvanted vaccine from Sanofi Pasteur), and 1 received an undetermined product. All of the narcolepsy cases were confirmed by sleep study tests, and 38 involved cataplexy episodes.

During France's pandemic vaccine campaign, about 4.1 million doses of Pandemrix and about 1.6 million vaccinations with Panenza were administered, according to the report.

Researchers found that 22 of the narcolepsy cases were in people 16 years old and older and 28 were in children 8 to 15 years old. Symptom onset occurred from 2 days to 15 months after vaccination. Eight patients—6 adults and 2 teens—had a medical or family history that might explain the condition.

The investigators reported that overall the same signal seen in Finnish and Swedish children was found in French children, but the link between Pandemrix and narcolepsy was also detected in French adults.

They cautioned that the findings don't show a causal relationship and that a more thorough investigation should be conducted to explore the link further, including possible environmental or genetic factors.

ECDC spokesman Giovanni Mancarella, in response to queries from CIDRAP News, said France is the only country in which an association between the pandemic vaccine and narcolepsy has been observed in adults, most of them younger adults. Though other countries have submitted adult cases to the wider ECDC study, based on the new French findings, they may reinvestigate them.

There are more than 100 suspected narcolepsy cases in adults reported in the European Medicine Agency's EudraVigilance database, the ECDC said.

Finland's National Institute for Health and Welfare (THL) said today that it is conducting further study on adult cases, according to a statement in Finnish posted on the group's Web site. It said the investigation will focus on 40 to 50 adult narcolepsy cases that were diagnosed between 2009 and 2011. About half of the patients had received the pandemic vaccine.

It's not clear why France is the only country that has found the association, Mancarella said, noting that with the data so far, it's impossible to show a causal relationship between the vaccine and narcolepsy in adults.

Yesterday's technical report included only part of France's data, and now that complete results have been submitted, Mancarella said, the ECDC will use it to look at the VAESCO case-control data again, with results expected in October.

See also:

Sep 20 ANSM statement and study (in French)

Sep 21 THL statement (in Finnish)

Sep 20 ECDC press release

Sep 20 ECDC technical report summary

Sep 20 ECDC full technical report

Sep 20 CIDRAP News story "ECDC studies shed new light on narcolepsy and H1N1 vaccine"