Monitoring scheme shows up resistant flu viruses 

April 2009

ESR Virologists at the WHO National Influenza Centre have identified influenza viruses resistant to oseltamivir, the active ingredient in Tamiflu.

Head of the centre, Dr Sue Huang said the discoveries were not unexpected as other countries have already had Tamiflu resistant strains.

“It was simply a matter of time before NZ found them as well. Identification of these resistant strains indicates the advantages of the excellent flu surveillance system run by the WHO National Influenza Centre at ESR. All the viruses identified with resistant characteristics are from the A group of circulating seasonal influenza viruses.

Staff at the centre established a test to monitor oseltamivir resistant influenza viruses as part of a national monitoring scheme. Oseltamivir is in a class of medications called neuraminidase inhibitors that are used in the treatment of influenza. They work by stopping the spread of the flu virus in the body.

Viral isolates from the New Zealand population, collected in the last three years from the national surveillance program were tested for susceptibility to Tamiflu. Four viruses of the specific strain influenza A(H1N1) analysed by the National Influenza Centre in 2008 were found to be resistant. A further resistant virus of the same strain has been identified in the first quarter of 2009. The results were reported to the World Health Organisation.

These results follow the worldwide situation where oseltamivir-resistant influenza viruses emerged in the Northern Hemisphere in January 2008.

As New Zealand is the first developed country in the world to allow the sale of Tamiflu over-the-counter, there is a global interest in the results generated from the monitoring scheme.