Serious questions have been raised about the safety of one of the vaccines used to fight the global H1N1 “swine flu” pandemic in 2009.

A report today in The BMJ claims new information is emerging, showing a striking difference in the number and frequency of adverse events reported for the vaccine in question, Pandemrix, compared with two others produced by the same company, GlaxoSmithKline (GSK), and approved for use across the world.

The report questions the transparency of information surrounding the safety of Pandemrix, and asks why the public has never been told anything.

According to The BMJ’s associate editor, Peter Doshi, internal safety reports from 2009 unearthed as part of a lawsuit suggest both GSK and health officials were aware of a variety of serious adverse events logged in relation to Pandemrix.

Doshi learned of the reports from colleague Tom Jefferson, who was an expert witness in a lawsuit alleging the vaccine caused the sleep disorder, narcolepsy. Jefferson used the information to calculate adverse event rates per vaccine, which showed large differences between Pandemrix and other GSK pandemic products.

The BMJ then conducted its own analysis and found that Pandemrix had, proportionally, five times more adverse events reported than Arepanrix and the other, unnamed, vaccine.

Doshi stresses the data are insufficient to draw cause-and-effect conclusions.

However, Gillian O’Connor, the solicitor involved in the narcolepsy lawsuit, says the disparity 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 the Pandemrix vaccination”.

The BMJ says GSK refers in many reports to having conducted “safety reviews”, but when asked for copies did not provide them.

The company also declined to answer questions – citing ongoing litigation – about whether it had ever notified healthcare providers about the discrepancies between its products or considered pulling Pandemrix from the market or recommending another of its vaccines.

The UK Department of Health also declined to comment on why it recommended Pandemrix over another company’s vaccine.