A new report is suggesting that significant resistance in Europe has built up against Roche’s influenza treatment Tamiflu.

Preliminary results from the study, carried out by experts at the European Centre for Disease Prevention and Control (ECDC), revealed that some of the H1N1 viruses in circulation this winter are resistant to Tamiflu (oseltamivir). It added that so far, 148 samples of influenza A viruses isolated during November and December from ten European countries have been tested by the EU-funded VIRGIL network and 19 showed evidence of resistance to oseltamivir.

The ECDC noted that 12 of the samples that tested positive for resistance to oseltamivir came from Norway, out of 16 sent for testing. In response, the Norwegian Public Health Institute immediately published an advisory notice to doctors and the public on its website that evening.

The ECDC, the European Commission and the World Health Organisation are currently assessing the significance of the data and an assessment will be published in the coming days. However they were at pains to note that “at this stage it is impossible to say what the level of resistance is in influenza across Europe”.

Nevertheless, the study claims that “the proportion of influenza viruses exhibiting resistance to oseltamivir must be significant, but not as high as in Norway”.

The ECDC trial results were revealed just as GlaxoSmithKline, maker of rival treatment Relenza (zanamivir), said it welcomes the new guidance from the European Medicines Agency on the use of antivirals during a flu pandemic and the recommendation that the availability of more than one antiviral would be useful.

The EMEA has stated that resistance has been observed more frequently, in particular amongst children, with increasing use of Tamiflu. However it highlights that, in contrast, viral resistance to Relenza is extremely rare.