W.H.O.

Systematic surveillance conducted by the Global Influenza Surveillance Network (GISN) including WHO Collaborating Centres (WHOCCs) for reference and research on influenza, continues to detect sporadic incidents of H1N1 pandemic viruses that show resistance to the antiviral oseltamivir. To date, 75 oseltamivir resistant pandemic H1N1 influenza viruses have been detected and characterized worldwide. All of these viruses show the same H275Y mutation. All these viruses remain sensitive to zanamivir. Worldwide, more than 10,000 clinical specimens (samples and isolates) of the pandemic H1N1 virus have been tested and found to be sensitive to oseltamivir.