Swine flu viruses grown in eggs to make vaccines don't produce as much volume as seasonal flu viruses, say scientists. (Reuters)

Human tests of a potential swine flu vaccine have begun, a spokesperson for Novartis said Wednesday, as other drug companies also prepared to start trials.

Novartis is testing a vaccine in a yearlong trial of 6,000 people of all ages in Britain, Germany and the United States, said Novartis spokesman Eric Althoff.

"We initiated clinical trials about 10 days ago," Althoff told The Associated Press.

A Briton received the first shot of H1N1 pandemic vaccine about 10 days ago, he said.

Novartis expects two doses will be required. The trial will also test this assumption.

Sanofi-Pasteur, which makes about 40 per cent of the world's flu vaccines, expects to start testing its swine flu vaccine within days in the U.S. and Europe, said spokesman Benoit Rungeard.

GlaxoSmithKline PLC, which has orders for 291 million doses of vaccine from countries including Britain and Canada, has not yet started testing its vaccine in humans.

Stretching supply

Last month, the Australian drug company CSL began human testing in Australia.

Manufacturers are comparing vaccines with and without adjuvants, the ingredients that are used to boost immune response so less vaccine is needed.

The World Health Organization recommends using adjuvants to maximize the global supply of swine flu vaccine.

Flu vaccines in Europe often contain adjuvants but Canada and the U.S. have not licensed flu vaccines with adjuvants before.

Last week, Dr. David Butler-Jones, the head of the Public Health Agency of Canada, said Canada will likely use adjuvanted vaccine as requested by WHO.

Health Canada wants GSK to conduct a small study to offer "minimum data on initial immunogenicity and some safety data if we're going for the adjuvanted vaccine," Dr. Elwyn Griffiths, director general of Health Canada's biologics and genetic therapies directorate, told The Canadian Press last week.

If U.S. politicians decide adjuvants are required, the Food and Drug Administration could also allow it under an emergency use authorization.

WHO and drug makers have said swine flu viruses grown in eggs to make vaccines are producing 25 to 50 per cent as much yield as seasonal flu viruses. WHO's laboratory network is trying to generate new vaccine viruses with higher yields.

AstraZeneca's MedImmune unit makes flu vaccine that is sprayed into the nose instead of injected. The company uses a different process to make vaccines than the traditional approach, and expects to start clinical trials in the U.S. around Aug. 17, Reuters reported.

With files from The Associated Press, The Canadian Press