Commentary
Delayed
H1N1
Tamiflu Resistance Reports in the United States
Recombinomics Commentary
03:05
November 19, 2008
Last year most of the Hong Kong (clade 2C) were in the Pacific region, and none had H274Y. All of the resistance was in Brisbane/59 (clade 2B), but the resistance was almost exclusively in a sub-clade that was closely related to the dominant sub-clade in northern Europe. That dominant sub-clade became more dominant over the summer in the southern hemisphere, which led to frequencies at or near 100% in many countries. The initial data in the UK, Norway, and Canada support a similar high level this season in the northern hemisphere.
Somewhat surprisingly, the resistance of only one H1N1 isolate was reported. It was negative and was said to be Brisbane/59-like. However, the antigenic analysis is not informative, because it is likely that both clade 2B and clade 2C will be called “Brisbane/59-like” even though the two sub-clades are readily distinguished when appropriate anti-sera is used. Last year all clade 2B and clade 2C were called “Solomon Island-like” even though there was no Solomon Island in circulation and proper anti-sera readily distinguish between clade 2A, 2B, and 2C, which is why the vaccine this season targeted Brisbane/59 instead of Solomon Island/3, which was the H1N1 vaccine target last season.
Thus, it is unclear what is in circulation in the US (or anywhere else in the world), because the H1 isolates are all being called “Brisbane/59-like” which produces a “match” with the vaccine, regardless of whether the isolate is clade 2B or clade 2C. Phylogenetic classification would be much clearer and more useful, but the current vaccine approaches are largely base on technology that is over 50 years old and in need of a significant upgrade.
Moreover, the current status of clade 2B and clade 2C will be clear when sequences are released because the phylogenetic analysis is very straightforward and easily distinguishes clade 2B from clade 2C, as well as sub-clades within these larger sub-clades.
When the NA sequences are generated, the Tamiflu resistance frequencies will be clear, which will lead to an evaluation of the current recommendations, which includes use of oseltamivir for all influenza infections.
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