Two New Zealanders expert in genetic shifts and mutations of
influenza strains say there is a risk that the swine flu
virus spreading out of Mexico may acquire resistance to
Tamiflu.
Also known by the chemical name oseltamivir, Tamiflu has been
stockpiled by the World Health Organisation (WHO), New
Zealand's Ministry of Health and governments worldwide for
use in the event of an influenza pandemic.
It slows the spread of the flu virus in the body and is a key
tool for protecting essential workers such as doctors and
nurses during the three months or more that it may take to
develop effective vaccines for a pandemic flu strain.
But resistance to the retro-viral drug is increasingly being
found in seasonal flu viruses in New Zealand - four last year
and one this year - in line with similar surveillance in
other southern hemisphere countries and the United States.
Dr Sue Huang, head of the WHO National Influenza Centre run
by New Zealand's Institute of Environmental Science and
Research, told NZPA the centre was monitoring oseltamivir
resistance to guide policy on the use of Tamiflu.
Dr Huang said from Geneva, where she is attending a WHO
meeting on national influenza centre contingency plans, that
it was "extremely important" to monitor oseltamivir
resistance because of the reliance being placed on Tamiflu
stockpiles in the event of a pandemic.
She warned there was a possibility that as the swine
influenza spread among people already exposed to
Tamiflu-resistant strains of influenza, the swine flu may
evolve resistance to the drug.
"Influenza virus is notoriously unpredictable," she said.
"It is very important to monitor closely in order to provide
early warning if (this) situation ... emerged."
New Zealand virologist Richard Webby, director of the WHO
collaborating centre for studies on the ecology of influenza
viruses in lower animals and birds at St Jude Children's
Research Hospital in Memphis, Tennessee, told NZPA the risk
of a Tamiflu-resistant swine flu evolving was a "valid
possibility".
"Flu viruses do exchange gene segments and it is possible
that the swine virus could swap out its neuraminidase (the
target for oseltamivir) with a human strain," he said.
Problems would arise if the resulting virus was able to grow
well and transmit between humans.
Dr Huang, based at the National Centre for Biosecurity and
Infectious Diseases at Lower Hutt, said that the Tamiflu
resistant strains of seasonal flu found in New Zealand had
all been from the influenza A family.
Strains resistant to oseltamivir emerged in the Northern
Hemisphere in January last year, and since then five viruses
of the A/H1N1 strain had been detected in New Zealand
patients, and reported to WHO.
According to the WHO, tests on H1N1 flu patients in 12
countries last year showed 31 percent had the H274Y mutation
associated with Tamiflu resistance.
Southern Hemisphere incidence of the mutation in tests on the
H1N1 virus ranged from 100 percent in South Africa to 13
percent in Chile.
Tamiflu is probably a paper tiger
Whether or not the current concern about a potentially lethal pandemic of swine ‘flu’ is justified, there are questions emerging about the potential comfort to be obtained from the extremely expensive and possibly fruitless massive stockpiling of the antiviral drug, Tamiflu.
We are told that swine ‘flu’ is caused by an influenza A (HINI) virus. In December last year the US Centres for Disease Control (CDC) told the world’s health professionals that a high proportion of this particular strain of virus was now resistant to Tamiflu (oseltamivir) antiviral medication.
http://www.cdc.gov/media/pressrel/2009/s090109.htm
More recently at beginning of March, a US Government report stated that over 98% of influenza A viruses were resistant to Tamiflu.
http://www.cbc.ca/health/story/2009/03/02/tamiflu-resistance.html
Yesterday we were all being reassured by the CDC that Tamiflu is probably effective in treating the outbreak of swine ‘flu’ affecting humans and being transmitted directly between humans. On what basis?
This is a question which requires a quick answer from our Government who appears to have slavishly accepted the advice of the CDC.