Increases in H1N1 Tamiflu and Relenza Resistance?
Recombinomics Commentary 20:58
September 25, 2008

Of 55 influenza A (H1N1) viruses that were collected and analyzed during May 18–September 19, one came from the United States, 44 from South America, five from Europe, and five from Asia.

Of the 86 influenza A (H1N1) viruses received from 14 countries and analyzed for oseltamivir resistance, 40 (46.5%) were resistant.

Only five of the influenza A (H1N1) viruses that were analyzed were from the United States; two of these viruses were resistant to oseltamivir.

Of these isolates, 185 were sensitive to zanamivir, and two required additional testing.

The above comments from tomorrow’s MMWR detail neuraminidase inhibitor resistance during the 2008 flu season in the southern hemisphere.  Most of these samples appear to be from South America and the levels of H274Y are 46.5%.  Moreover, almost all are the Brisbane/59 strain, raising concerns that the strain will reappear in the upcoming season in the northern hemisphere.

Although the level was below the 100% recorded for South Africa and Australia, the level is markedly higher than the level recorded for Europe last season, providing additional evidence for selection of Brisbane/59 sub-clade(s) carrying H274Y.

Moreover, the additional testing on two of the isolates for zanamivir (Relenza) resistance, raises concerns that the two isolates in the United States (Pennsylvania and New Jersey), which were mixtures of wild type and Q136R/K, represented the early emergence of Relenza resistance in Brisbane/59.

The publishing of a MMWR report by the CDC in the northern hemisphere’s “off” season, highlights the concern over the increasing resistance to neuraminidase inhibitors, Tamiflu and Relenza.  These anti-virals are the first line defense against pandemic influenza, and the increasing levels of resistance in H1N1, which has homology with the N1 in H5N1, remains a cause for concern.

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