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Tamiflu Resistance in UK Increases to 96%
The above comments are from the week 47/48 report from England and indicate that four more H1N1 isolates have been tested for H274Y, and all four are positive. Thus, the UK levels for H1N1 from England, Wales, and Scotland are above 96% (25/26). In addition, all H1N1 isolates from Norway and Austria have H274Y, indicating H274Y is fixed in H1N1 (clade 2B) in Europe.
Similar results have been obtained for North America. The one H1N1 sample from Canada has H274Y, as do 24/25 isolates in the United States, indicating H274Y is also fixed in North America.
This fixing has a smaller impact in Europe, because most of the influenza A reported this season in EISS has been H3N2, although H1N1 is dominant in Russia. In contrast, 85-90% of the influenza A in the United States has been H1N1, which creates a mismatch on antiviral recommendations. Amantadine resistance is fixed in H3N2 and use has been discouraged, although H3N2 represents only 10-15% of influenza A. In contrast, oseltamivir (Tamivir) is recommended, even though the vast majority of influenza A is resistant, since H274Y is fixed in H1N1.
The CDC has requested additional samples, but the fixing of S31N in H3N2 and H274Y in H1N1 is unlikely to change in the near term, and until frequencies of H3N2 increase significantly, the antiviral recommendations in the United States will remain mismatched with the influenza A in circulation.