By Sam Cage

ZURICH, Sept 3 (Reuters) - Novartis's vaccine against H1N1 swine flu gave a strong immune response even after one dose in a pilot trial, the Swiss drugmaker said on Thursday.

The trial with 100 volunteers run by Britain's Leicester University showed a potentially protective immune response in 80 percent of subjects after one dose and more than 90 percent after two doses, Novartis said in a statement.

'The study suggests that while two doses seem to provide better protection, one dose of our adjuvanted Celtura vaccine may be sufficient to protect adults against the swine flu,' said Andrin Oswald, chief executive of Novartis vaccines unit.

Although the strain seems mild at present health officials are worried it might return in a more virulent form in the northern hemisphere winter. The flu is the first to be declared a pandemic since 1968.

Experts have predicted that two shots will be needed to provide swine flu immunity but last month China's Sinovac Biotech, the first company worldwide to complete clinical trials for an H1N1 vaccine, said a single dose of its vaccine proved sufficient.

Sinovac also said on Thursday it has received approval from the Chinese health authorities to mass produce a vaccine against H1N1.

Officials are concerned that supplies of vaccine will prove tight but a need to vaccinate people only once instead of twice would stretch out stocks substantially.

Novartis is already carrying out more clinical trials, which will include more than 6,000 adults and children.

Pharmaceutical companies around the world, including Sanofi Aventis, GlaxoSmithKline, CSL and AstraZeneca's MedImmune unit, are racing to develop H1N1 vaccines.

The Novartis vaccine, called Celtura, was well tolerated by the volunteers, with pain at the injection site the most frequent complaint.

Novartis said more trials were already under way around the world, including more than 6,000 adults and children but did not give any details on when the vaccine would be widely available.

(Additional reporting by Emma Thomasson; Editing by Ben Hirschler, Greg Mahlich)

(Zurich Newsroom, zurich.newsroom@reuters.com, +41 58 306 7336)

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