Clinical trials began in the Australia this week on a vaccine to thwart a possible flu epidemic of the virus that has so far killed more than 700 people worldwide. Similar trials will soon begin in the United States in the hopes of producing a vaccine in time for flu season. Two separate seven-month trials to test a possible swine flu vaccine in Australia began on Monday and Wednesday; the studies have 300 and 240 subjects, respectively. Because it's winter in the Southern Hemisphere, and therefore flu season, Australian authorities said it was important to test vaccines there as soon as possible.