"...As of late last week the World Health Organization was reporting that 42 cases of Tamiflu-resistant pandemic H1N1 viruses had been seen globally since the pandemic began."
"...I have to admit I would have expected more cases, considering ... the large volume of Tamiflu that has been used in the last few months, certainly more than in the last five years, probably," said Boivin..."
As at the end of October only 12,579 samples of flu had been tested for tamiflu-resistance. The percentage of resistant samples was 0.3%, varying from 0.2% in Europe to 0.5% in the Western Pacific.
This is basically background as during the initial clinical trials of tamiflu about 0.3% of samples were resistant.
At a rough guess, of the estimated 10m cases of the flu to-date 0.3% or 30,000 cases could be expected to be resistant.
Recent sampling in the US shows a significant increase to 1.6%. This however may be due to sampling bias - those with compromised immune systems are sampled more and the delay in the body clearing the flu in these patients leads to resistance.
The development of Oseltamivir resistance in SEASONAL flu was very similar to the development of Adamantane resistance, it went from background in flu season 1, to around 10-15% resistant by flu season 2 to almost total in flu season 3 (world-wide data).
The difference between seasonal and pandemic flu on resistance is not known.
Secondly. There are cases of resistance developing as a result of taking low dose preventative tamiflu. The case for broad resistance developing is less clear.
During the 2007-2008 influenza season. For example, oseltamivir resistance among H1N1 strains was 67.3% in Norway, where oseltamivir is rarely used, but was only 3% in Japan, the country with the highest per capita oseltamivir use.
It is believed that the H274Y mutation also lead to the flu strain being "fitter" beyond that of tamiflu resistance.
