# 3814
Oseltamivir (Tamiflu) is our first line of antiviral defense against the novel H1N1 `swine’ flu virus. And by all accounts it remains effective for the vast majority of cases.
But scientists are concerned that this virus – like its seasonal H1N1 cousin – could mutate into a Tamiflu resistant strain. That would severely cripple our ability to treat serious cases of this flu, as the only other antiviral in our arsenal is the inhaled powder Relenza (Zanamivir).
The number of resistant cases detected thus far are very small. Fewer than 3 dozen worldwide. The real number is no doubt higher, however, as only a tiny fraction of viruses are tested.
Japan has now reported 8 cases, with the latest found in a teenage girl who had not received the drug.
First the story from Reuters, then some discussion.
Japan Tamiflu-resistant H1N1 teen had no Tamiflu record
Thu Oct 8, 2009 8:41am IST
TOKYO (Reuters) - A genetic mutation of H1N1 swine flu that is resistant to the antiviral drug Tamiflu has been detected in a Japanese teenager who had not previously been treated with the drug, a Japanese health official said.
The case could mark Japan's first instance of person-to-person transmission of a Tamiflu-resistant strain of the H1N1 flu but Health Ministry official Takeshi Enami said there was still insufficient evidence to confirm that.
"We cannot deny that this could be person-to-person transmission, but we are not able to reach that conclusion," Enami said. Japan has had eight cases of new H1N1 patients who were resistant to Tamiflu, he added.
A certain amount of `spontaneous’ resistance to Tamiflu (among those taking the drug) is to be expected, according to Roche – the makers of the antiviral.
This from their FactSheet on Tamiflu.
Data collected from around 4000 people treated with Tamiflu demonstrate that resistance is very infrequent. The overall incidence of resistant virus of 0.32% in adults and 4.1% in children aged one to 12. This resistant virus was found to be less virulent than the wild type virus and did not affect the course of the illness.
We’ve heard assurances from the WHO that resistant strains are less `biologically fit’, and unlikely to be transmissible. This from Bloomberg News just 3 weeks ago.
Swine Flu That Resists Tamiflu Is Harder to Spread, WHO Says
By Michelle Fay Cortez
Sept. 15 (Bloomberg) -- Swine flu that can resist treatment with Roche Holding AG’s Tamiflu is also harder to spread to other people, according to World Health Organization officials.
Almost two dozen people have developed swine flu infections that don’t respond to Tamiflu, a mainstay of therapy for the outbreak that began in April. The genetic mutation that helps the virus evade the drug also thwarts its transmission, so the infection isn’t passed on to other patients, said David Mercer, acting head of the communicable diseases unit of the WHO’s European region.
Perhaps.
But this is eerily similar to the reassurances we got 3 years ago when rare reports of resistance in seasonal H1N1 began to emerge.
Today, nearly all seasonal H1N1 viruses are resistant to Tamiflu. So much for it rendering the virus `unfit’ to transmit.
Over the summer the CDC has tested 1865 samples of the novel H1N1 virus, looking for resistant strains. They’ve found 9 total. (note:link is to latest numbers, which will change over time).
Which brings us back to the new report from Japan. Unlike most of the cases we’ve seen reported, this one involves a patient who was not receiving the antiviral Tamiflu.
Which suggests this mutation probably occurred in someone else who was taking the antiviral, and that this mutated virus was `biologically fit enough’ to be passed on to others.
I say `suggests’ because it is impossible to know with certainty.
In July Investigators in Hong Kong reported a similar case of a woman with a resistant strain who also had not taken the drug, which raised alarm bells.
At the time, Helen Branswell of the Canadian Press reported in her article Tamiflu resistant H1N1 from Hong Kong more worrying than earlier findings some of the reaction from the scientific community, including this quote:
"It was not at all surprising to see resistance in patients on treatment but seeing it in someone who was not treated, it certainly is more concerning," says Dr. Malik Peiris, a flu expert at the University of Hong Kong.
Signs of increasing resistance, particularly among patients who have not received the drug, are of genuine concern. Not so much for the way we treat patients today, but for the impact it may have down the road.
For now, the incidence of Tamiflu resistance appears quite low, and most appear to be of the less worrisome `spontaneous’ type of mutation that can occur in patients taking the drug.
But the recent history of seasonal H1N1, which went from highly susceptible to highly resistant to Tamiflu in one season, linger in the minds of most scientists watching this situation.
Which is why reports such as this one, while still rare, cause those of us who follow the virus to sit up and take notice.
