Cervarix on top in head-to-head, but how meaningful?

The first comparative study of the two licensed human papillomavirus (HPV) vaccines, Cervarix and Gardasil (HPV types 6, 11, 16, 18 recombinant vaccine), has shown that the former generated a significantly higher immune response as measured by neutralising antibodies (Abs) and memory B-cells.

Although GlaxoSmithKline has touted these results as highly positive, others have hit back claiming that the trial is meaningless as it did not look at which vaccine was more effective at preventing actual cases of cervical cancer or precancerous lesions. This would require a longer and larger trial, which GSK has said it has no plans to conduct. Instead, the company hopes that the head-to-head study will boost the profile of Cervarix, which is yet to be launched in the US and is trailing Sanofi Pasteur MSD's (sanofi-aventis and Merck & Co joint venture) Gardasil in global markets.

Meanwhile, recent data on Gardasil have shown that the vaccine offers protection from certain HPV strains for up to 9.5 years; previously, data only showed its effects for five years. In another study, Gardasil reduced the number of abnormal Pap tests and cervical procedures. However, with Gardasil's US sales falling and Cervarix not even on the market yet in that territory, can the comparative trial data make a difference in revenues for GSK?

Gardasil, which was first to market, and launched in the US and Europe in 2006, generated sales of US$1.4 billion in 2008, while Cervarix brought in just US$231 million. Cervarix is still awaiting US marketing approval, and has only been adopted as the vaccine in national immunisation programmes for two European countries, the UK and the Netherlands. The FDA refused to approve Cervarix until GSK provided more clinical information, but the company expects approval to come later this year.

So what of the new comparative data? The presence of Abs is a first indication of the body's ability to protect itself against disease, but this does not necessarily mean Cervarix could prevent more infections than Gardasil. The study showed that Cervarix provided significantly higher neutralising Ab levels than Gardasil: more than two-times higher for HPV type 16 and more than six-times higher for HPV 18. For both virus strains, Cervarix also induced 2.7-times more memory B-cells, another important element of the immune system.

According to GSK, the study "offers the first evidence that these two vaccines do not generate the same immune response against HPV types 16 and 18, the two most common cancer-causing virus types". Its competitor was dismissive of the data, with Bennett Lee, Medical Director for Gardasil at Sanofi Pasteur MSD commenting: "We see no clinical relevance in the results of this study ... and we don't see the point of doing such a comparison. If you want to compare vaccines, you compare clinical efficacy". However, the final word will come from doctors and patients when, and if, Cervarix is licensed in the US later this year.

Matthew Dennis - Editor, Cancer Drug News