Swiss pharmaceutical giant Roche has backed the use of its antiviral drug Tamiflu as a preventive treatment for pandemic flu, especially for those most exposed to the virus.

"Tamiflu is an antiviral, it is not a vaccine, but it can be used both for preventing and treating influenza," said David Reddy, head of Roche's pandemic task force.

Reddy said during a news conference that the drug, which is one of the recommended treatments for those suffering from the new A(H1N1) influenza, had value as preventive treatment for groups that are most exposed to the virus, such as health staff.

While the World Health Organisation regards a vaccine as the main form of prevention, it has not excluded prophylaxis with a daily half dose of Tamiflu, he added.

William Burns, chief executive of Roche's pharmaceutical division, told AFP that such prophylactic use might be warranted in some particular cases, such as the mothers of children who are ill or in nursing homes where cases of H1N1 flu had appeared.

However, he added: "The first line of the prevention is the vaccine, and the first line of treatment is Tamiflu."

Former Roche France director Pierre Bonnet said several governments were debating the preventive use of the drug, and their choice could be dictated by the severity of local outbreaks and the timing of vaccine delivery.

Burns said production capacity of the antiviral drug was still much larger than current demand.

Some 96 countries had ordered 270 million doses since 2004, according to figures compiled in July.

Roche had 100 million doses in stocks in March, before the emergence of the new H1N1 pandemic virus.

The strain of pandemic flu is sensitive to two drugs, oseltamivir -- the basic ingredient of Roche's Tamiflu -- and zanamivir in rival GlaxoSmithKline's drug Relenza, according to the WHO.