INFLUENZA VIRUS - RELENZA RESISTANCE LABORATORY MUTATION

Date: Tue 4 Aug 2009
Source: The Age [edited]



Relenza-resistant flu virus mutation found
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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 flu virus [Influenza pandemic (H1N1) 2009 virus] or
bird flu [avian influenza H5N1) virus], and it was found only in the
lab [i.e., only after propagation of patients' samples in the
laboratory], 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 [2008], 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 [i.e., the isolates screened
were all seasonal influenza viruses - Mod.CP]. 9 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 [see below].

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 mutated virus 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
[influenza pandemic (H1N1) 2009] virus infection and rising demand
from government stockpiles.

Last week Japan identified its 3rd case of Tamiflu-resistant swine
flu, making a total of 6 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.

[Byline: Nick Miller]