GlaxoSmithKline’s H1N1 swine flu vaccine Pandemrix made waves around 2010 after increased cases of narcolepsy emerged in Sweden and Finland among children who got it during the previous pandemic. But a recent report by The BMJ suggests greater safety problems with the vaccine, which neither GSK nor health authorities have made public.

After examining several GSK-made internal safety reports obtained through an ongoing lawsuit alleging that Pandemrix caused the sleep disorder, the medical journal found a large discrepancy in adverse event rates dated years back between Pandemrix and two other GSK pandemic vaccines. Pandemrix have not been available for several years now.

Specifically, by Dec. 2, 2009, for each million doses of vaccine administered, about 76 cases of serious adverse events were reported for people who got Pandemrix, while 8 were for Arepanrix and another unadjuvanted vaccine combined. The pattern continued for the next eight reports seen by The BMJ, and by the end of March 2010, the rate for Pandemrix was 72, seven times that for Arepanrix and the third vaccine combined.

The journal cautions that the numbers themselves are not sufficient to draw any causal relationship. But what it finds more problematic is that neither GSK nor health authorities seemed to have made the information public.

"[They] raise fundamental questions about the transparency of information," about when the public should be alarmed of possible harms of vaccines detected through pharmacovigilance, Peter Doshi, an associate editor of The BMJ, wrote in his report.

In response to a FierceVaccines request for comment, GSK said: "Throughout the development and introduction of the Pandemrix and Arepanrix vaccines GSK fulfilled all requirements established by the authorities for the monitoring and evaluation of safety data. During the pandemic, GSK conducted enhanced evaluation of safety data and supplied all safety data and the company’s assessment to EMA and other authorities, summaries of which were made available to the public weekly on the EMA website."

The disparity in adverse events reported was "of such striking difference that any person contemplating taking the Pandemrix vaccine would be likely, if in receipt of this information, not to choose to have [it]," Gillian O’Connor, the solicitor representing an Irish woman who’s suing GSK and health agencies, wrote in an affidavit filed in court.

Both Pandemrix and Arepanrix contain an oil-in-water emulsion adjuvant called AS03, but different methods are used to prepare the hemagglutinins used in them.

Pandemrix’s EU approval, first granted on Sept. 25, 2009, along with Novartis’ Focetria and Baxter’s Celvapan, has expired in August 2015 as GSK didn’t apply for a renewal "due to lack of demand," according to an EMA statement (PDF). Arepanrix was approved in Canada in October 2009 but wasn’t in EU until the next March, at the tail of the pandemic, and its marketing authorization was voluntarily withdrawn at the request of GSK in late 2010.

It was not clear how much the EMA knew about the safety profile of those vaccines. But a press release from the agency in July 2011 said after considering all available data, including analysis of safety surveillance data performed in several member states and case reports from across the EU, its Committee for Medicinal Products for Human Use "confirmed that overall the benefit-risk balance of Pandemrix remains positive."

"While it might have been possible to estimate reporting rates based on usage data, which are difficult to obtain during a pandemic, EMA does not have a methodology to compare reporting rates between two products (note that the pandemic influenza pharmacovigilance updates included number of reports, not rates)," an EMA spokesperson said, as quoted by The BMJ.

Neither Pandemrix nor Arepanrix has ever been greenlighted in the U.S. Instead, the FDA waved through four nonadjuvanted H1N1 vaccines by CSL, GSK, Novartis and Sanofi Pasteur. In a response to the narcolepsy reports following immunization with Pandemrix, the CDC carried out a population-based study and found the FDA-approved 2009 H1N1 flu shots were not associated with an increased risk for the neurological disorder.

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