THE H1N1 flu virus has mutated into a form resistant to the Australian-developed antiviral drug Relenza.
Researchers said the mutation posed little threat to humans yet: the virus was not a strain of swine or bird flu, and it was found only in the lab, not in patients.
There are no known strains of Relenza-resistant influenza in humans. In contrast, virtually all the flu cases in the US and Europe last year, much of Australia’s seasonal flu and even a few cases of swine flu have proven resistant to the other leading antiviral drug, Tamiflu.
A team at North Melbourne’s WHO Collaborating Centre for Reference and Research on Influenza analysed 391 influenza A(H1N1) viruses found in humans in Australasia and South-East Asia between 2006 and 2008, before the spread of swine flu.
Nine of the viruses had a previously unseen mutation that made them 300 times more resistant to zanamivir (sold as Relenza), according to results reported in the Journal of Virology.
The mutation was not found when the specimens were taken from patients, only later when the viruses multiplied in the lab.
‘‘That could mean there were very low levels of this mutation in the patient,’’ said Dr Ian Barr, one of the researchers involved and deputy director of the WHO centre. ‘‘We wouldn’t say it’s a clinical problem, but it’s an interesting finding. We know [the mutation] can survive, and it’s stable.’’
The recent spread of Tamiflu-resistant A(H1N1) viruses showed that antiviral-resistant viruses could spread rapidly and travel widely around the world, the study authors warned.
A spokeswoman for Biota, which developed Relenza, said the discovery was ‘‘not clinically relevant, because it’s an in vitro discovery — there’s no evidence that this mutation has infected patients’’.
A spokeswoman for Relenza manufacturer GSK said the ‘‘clinical significance is yet to be determined’’.
GSK announced a week ago that it planned to triple production of Relenza in the face of the spread of swine flu and rising demand from government stockpiles.
Last week Japan identified its third case of Tamiflu-resistant swine flu, making a total of six worldwide.
Scientists have warned that the massive worldwide use of Tamiflu since the outbreak of swine flu could hasten the spread of resistant mutations. No Relenza-resistant swine flu has yet been found.
