TORONTO - Health Canada has given pharmaceutical giant GlaxoSmithKline permission to market its flu drug Relenza for the prevention of influenza, not merely the treatment of the illness.

The Canadian approval, announced by GSK on Thursday, follows in the footsteps of similar approvals by regulators in the United States and 15 European Union countries.

Other flu drugs on the market here - Tamiflu and the generic drug amantadine - were already approved for prevention of influenza.

One might consider taking a flu anti-viral for prevention or prophylaxis, as it's called, if a member of a household comes down with infectious virus and others want to avoid getting sick. As well, flu drugs are often used on a preventative basis to protect vulnerable seniors in long-term care facilities during flu outbreaks.

GSK, the world's second biggest manufacturer of flu vaccine, also announced Thursday it had entered into a contract to provide flu vaccine to Denmark in the case of a pandemic.

Denmark has agreed to buy 4.6 million doses of a vaccine, enhanced with GSK's unnamed proprietary adjuvant, for an undisclosed price.

Adjuvants are chemicals that boost the immune response induced by a vaccine. Adding them to vaccine allows a smaller dose to achieve an equal or greater immune response than a dose of unadjuvanted vaccine - a feature that could be critical in a pandemic, when demand for vaccine will far outstrip supply.

The vaccine for Denmark will be made in GSK's European manufacturing facilities, the company said in a release.

Canada was the first country to sign a deal with a vaccine manufacturer for pandemic vaccine. The 10-year deal, signed in 2001, requires the designated manufacturer to be at the ready to produce pandemic vaccine at all times.

The contract was initially signed with Shire Biologics. When Shire sold its Quebec-based flu vaccine operations to ID Biomedical in 2004, that company acquired the pandemic contract. But in the fall of 2005 GSK bought IDB's vaccine production operations, becoming Canada's pandemic vaccine manufacturer.