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Israel's Central Laboratory for Viral Infections has identified a strand of H1N1 that showed signs of resistance to the Tamiflu drug used to treat swine flu, the Health Ministry said Thursday.

The strand was isolated from a sample taken from a swine flu patient in a high risk group that completely recovered from the virus.

The ministry said laboratory tests were continuing and the findings were being evaluated. It noted that resilient forms of the virus have already been discovered elsewhere in the world.

Tamiflu and Relenza were the only two medications that had thusfar proven effective in treating the virus (also known as H1N1), which already proved resistant to other seasonal flu remedies.

Tamiflu had been particularly popular, as it is ingested orally. Relenza, which is inhaled, is therefore not recommended for patients with respiratory conditions. Both drugs work by disabling an enzyme the virus needs in order to grow. Many governments in the world, including Israel's, have stockpiled Tamiflu in large quantities since the swine-flu pandemic began.

Reports of Tamiflu-resistant strains of swine flu began in late June.

Earlier studies on Tamiflu indicated that 0.4 percent of adults and 4 percent of children afflicted with normal seasonal flu were likely not to respond to the drug.