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H1N1 Tamiflu Resistance in England Approaches 100%
Recombinomics Commentary 12:37
November 27, 2008

Fourteen of fifteen A (H1) specimens tested in the same time frame are
resistant to oseltamivir but sensitive to zanamivir and amantadine. The majority of these resistant viruses come from the south west of England with the remaining from Wales and northern England. Two influenza A (H1) isolates have been found to be resistant to oseltamivir in Scotland this season. Four further influenza A(H1) isolates are undergoing resistance testing at the moment.

Since week 40/08 57 viruses have been characterised: nine A/Solomon Island/3/2006 (H1)-like which is similar to the vaccine strain, two A (H1) Brisbane/59/2007 (H1N1)-like (vaccine strain) and 46 A (H3) A/Brisbane/10/2007 (H3N2)-like (vaccine strain).

The above comments from this week’s influenza report from England indicate two additional isolates (from Wales and northern England) have been tested and both had H274Y.  The four additional H1N1 isolates are being tested.  Thus, since the report of 9/10 resistant isolates in England, 5/5 isolates in England have H274Y, as do 2/2 isolates from Scotland, indicating resistance levels are approaching 100%.

Similar results are being reported in the United States, where 19/19 of the most recently reported results also have H274Y.  Both countries reported resistance levels close to 10% of H1N1 last season, so the increase to almost 100% is dramatic, but not unexpected, because similar levels were seen over the summer for several countries in the southern hemisphere, with South Africa being the most notable with H274Y in all 215 H1N1 isolates tested.

Although there was some heterogeneity in the South Africa isolates, all traced back to the Brisbane/59 sub-clade that was dominant in Europe and the United States.  The above serological characterization of the H1N1 in England may reflect this heterogeneity, but release of the sequences would allow for phylogenetic analysis which demonstrated that the Solomon Island strain (clade 2A) was not circulating last year and is unlikely to be circulating this year.  However, further evolution of the dominant Brisbane sub-clade, or emergence of new sub-clades is expected, since there were multiple introductions of H274Y onto Brisbane genetic backgrounds last season, which was most common in Japan, but present worldwide.  Moreover, Hong Kong released three clade 2C sequences with H274Y, raising concerns that H274Y levels in clade 2C were also on the rise this season.  Over the summer, H274Y levels in H1N1 rose to more than17%, while amantadine resistance levels rose to 70% in Hong Kong.

Release of sequence data for H1N1 in Engalnd and the United States would be useful.

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