Swine Flu: First Case Of Tamiflu-Resistant H1N1 In Denmark

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First H1N1 swine flu patient was found to be resistant to Tamiflu (Oseltamivir) treatment in Denmark. Tamiflu is an anti-viral drug of choice against influenza infections that reduces the severity of symptoms and limits the spread of the virus when administered early. The drug is manufactured by Roche Holding AG. Influenza virus resistance to Tamiflu has been observed before, but it is the first case of Tamiflu resistance in the 2009 H1N1 virus. Typically, influenza infections that last longer as is the case with novel viruses, such as the 2009 strain of H1N1, are more prone to developing resistance because the virus has more time to change its genetic code to adapt to the anti-viral drug.

The news of resistance to H1N1 may be of concern to the World Health Organization (WHO) that raised the flu pandemic alert level to phase 6 signaling the onset of worldwide pandemic on June 11, 2009. However, Roche representatives have issued a statement, saying that the first case of H1N1 resistance in Denmark was ad hoc, and does not imply that the entire H1N1 virus strain is now resistant to Tamiflu. They said that the patient who developed resistance to the drug had done so during treatment. The resistance was "drug-induced" and "[not] naturally incurring, where a virus strain in itself is not responding to the drug," according to Roche representatives. Roche thus claims that Tamiflu still works and expects WHO to continue to back the use of the drug. Nothing has been said about the development of resistance to a similar acting anti-viral drug Relenza (Zanamivir). Some experts say Relenza might be more effective for keeping the 2009 strain of H1N1 in check because there is a seasonal strain of H1N1 that is widely resistant to Tamiflu.

The target of Tamiflu and Relenza anti-virals is the viral enzyme called neurominidase, which clips off virions from infected cells allowing influenza virus to disperse. However, a mutation in neurominidase that renders virus resistant to Tamiflu might also cripple the virus by giving it a less-functional enzyme. This means that a Tamiflu-resistant strain might actually have lower infectivity and virulence. So, it will be unreceptive to the drug treatment, but might not cause as much damage.

If the 2009 H1N1 strain was to become resistant to Tamiflu bur remain just as virulent, the prodigious stockpiles of the anti-viral drug that many governments made in the wake of the pandemic alert will be quite useless, leaving us with fewer options to treat the infection on pandemic level.