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Deadly H7N9 Bird Flu May Resist Tamiflu Vaccine

Virus shows rapid resistance to neuraminidase inhibitors (May 28)

In an article published online in The Lancet, doctors in Shanghai and Hong Kong report that the deadly H7N9 avian influenza virus, which has claimed 39 lives, may be resistant to the widely used Tamiflu vaccine.

The authors studied 14 patients with A/H7N9 infection admitted to the Shanghai Public Health Clinical Center, China, between April 4 and April 20, 2013. All of the patients had received antiviral treatment with a neuraminidase inhibitor — Tamiflu (oseltamivir, Roche) or the investigational agent peramivir (BioCryst Pharmaceuticals) — for fewer than 2 days before admission. Neuraminidase inhibitors offer the only known treatment option for influenza virus infection.

Specimens of viral load were obtained from the patients’ throat, stool, serum, and urine. The specimens were then sequenced for viral RNA to study the mutations associated with resistance to neuraminidase inhibitors and their association with disease outcome.

Three of the 14 patients had persistently high viral load in the throat in spite of antiviral therapy. The authors identified an Arg292Lys mutation in the virus neuraminidase gene known to confer resistance to both oseltamivir and zanamivir (Relenza, GlaxoSmithKline) in two of these patients, both of whom had also received corticosteroid treatment. In one of the patients, wild-type sequence Arg292 was noted 2 days after the start of antiviral treatment, and the resistant mutant Lys292 dominated 9 days after the start of treatment.

“The apparent ease with which antiviral resistance emerges in A/H7N9 viruses is concerning; it needs to be closely monitored and considered in future pandemic response plans,” the authors cautioned.

Source: Lancet; May 28, 2013.

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