Washington, July 23 (DPA) The US is to start clinical trials of two vaccine candidates for swine flu, which has killed over 700 people worldwide, the National Institutes of Health (NIH) said Wednesday.

Eight university research hospitals will be involved in the trials, which will be compressed as the US races to have a vaccine ready before the possible resurgence of the A-H1N1 influenza in the fall, when the flu season is in full swing in the northern hemisphere.

The trials are expected to begin 'in the very near future', the NIH said, without providing a specific date. This is likely to be mid-August.

After the isolation of the swine flu virus, which emerged in Mexico and spread rapidly across the world, the US Centres for Disease Control and Prevention distributed a seed virus to vaccine manufacturers to develop vaccine pilots for testing.

Initial studies will look at whether one or two 15-microgram doses of H1N1 vaccine are needed to induce an immune response in healthy adult volunteers (18 to 64 years) and elderly people (65 years and older).