Researchers found no credible evidence that either Roche Holdings’ Tamiflu or Biota Holdings’ Relenza would be effective against avian influenza, according to a study published in The Lancet magazine.Also, Tamiflu and Relenza should not be prescribed routinely for seasonal flu symptoms, the study by Tom Jefferson, a researcher with the Cochrane Vaccine Fields in Rome, says.Instead the drugs, known as neuraminidase inhibitors, should be reserved for use against a serious outbreak of seasonal flu or pandemic flu.Governments around the world are ordering doses of Relenza and Tamiflu to stockpile in the event of a flu pandemic as bird flu spreads in Asia and threatens Europe. GlaxoSmithKline, which markets Relenza, and Roche have reached out to other makers to help increase supplies.