Systematic surveillance conducted by the Global Influenza Surveillance Network, supported by WHO Collaborating Centres and other laboratories, continues to detect sporadic incidents of H1N1 pandemic viruses that show resistance to oseltamivir. To date, 28 resistant viruses have been detected and characterized worldwide.[2] http://www.who.int/csr/disease/swineflu/notes/h1n1_antiviral_use_20090925/en/index.html