# 5786
Since it first appeared in the spring of 2009, scientists have worried that the H1N1 swine flu would someday develop resistance to the antiviral medication oseltamivir (Roche’s Tamiflu ®) as its predecessor - seasonal H1N1 - did in 2008.
Overall, however, the news has been generally good.
During the first two years, only 1%-2% of samples tested have shown the most common mutation known to convey oseltamivir resistance; H275Y, where a single amino acid substitution (histidine (H) to tyrosine (Y)) occurs at the neuraminidase position 275.
(Note: some scientists use 'N2 numbering' (H274Y) and some use 'N1 numbering' (H275Y))
Most of these cases of antiviral resistance occurred spontaneously in people after being treated with the drug, and quite often involved immunocompromised individuals.
Yesterday, ProMed Mail published a report from Australia on an unusual and worrisome cluster of oseltamivir resistance in New South Wales. More than 2 dozen patients – roughly 14% of the isolates tested from that region since May – have shown the H275Y mutation.
INFLUENZA (50): AUSTRALIA (NEW SOUTH WALES), H275Y MUTATION CLUSTER
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A ProMED-mail post
http://www.promedmail.org
ProMED-mail is a program of the
International Society for Infectious Diseases
http://www.isid.org
Date: Thu 24 Aug 2011
From: Kate Hardie
A cluster of oseltamivir-resistant A(H1N1)2009 influenza cases with onset between May and August 2011 has been detected in the Hunter region of New South Wales (NSW), Australia.
Viruses from 25 of 184 (14 percent) A(H1N1)2009 cases from the Hunter New England region exhibited highly reduced oseltamivir sensitivity due to the H275Y substitution in the neuraminidase. The H275Y mutation is a well-established substitution previously reported to confer oseltamivir resistance in N1 neuraminidases and was present in the widespread oseltamivir resistant pre-pandemic seasonal A(H1N1) virus.
Significantly, none of the cases reportedly took the antiviral prior to their flu test, and in follow up interviews with 16 of these cases, none have a history of being immunocompromised.
Jason Gale, writing for Bloomberg News, has more details, including some quotes from World Health Organization officials on this finding.
Tamiflu-Resistant Flu Outbreak Reported in Australia’s Newcastle, WHO Says
By Jason Gale - Aug 25, 2011 9:25 PM ET
For now, the H1N1 virus remains overwhelmingly sensitive to oseltamivir, even in the New South Wales region where all of these cases are located. And the H1N1 virus with the H275Y mutation remains sensitive to GSK’s Relenza, an alternative antiviral.
The concern is that this appears to be a biologically fit, easily transmitted strain of H1N1 and that it might eventually spread beyond this region.
Which is exactly what we saw happen with the old seasonal H1N1 virus, when in early 2008 Norway began to report a rise in resistant samples, and less than a year later the resistant strain was the predominant strain around the world.
It’s a crowded viral field out there, and whether this resistant strain can compete with the numerous non-resistant strains of H1N1 on the global stage is something we will have to wait to see.
This is a compelling enough reason, however, to get that seasonal flu shot this year. It is better to try to prevent the flu, than to have to treat it.
Photo Credit PHIL
Particularly if treatment options should become more limited in the future.
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