Two Australian biotechnology companies have started inoculating adult volunteers in the world's first H1N1 swine flu vaccine trials, with the hope of producing an effective shot against the virus that has so far killed more than 700 people worldwide.

Adelaide-based Vaxine initiated trials Monday with 300 participants, while Melbourne's CSL has 240 people in its seven-month study. Australia had 14,703 confirmed cases of swine flu as of Wednesday, and at least 41 deaths, according to the Associated Press. The winter flu season is well under way in the Southern Hemisphere.

"We're right in the middle of a surge of swine flu cases where perhaps the United States won't have to worry about it as much until their flu season hits in six months," Vaxine research director Nikolai Petrovsky told the AP.

But Petrovsky told BBC News that there "is no guarantee any of these vaccines will work. Swine flu is a very peculiar beast, it's a very different virus that we're dealing with. But we are hopeful."

Both companies said it would be at least six weeks before results of the initial trials are known.

"We have a specific vaccine that we believe will be able to protect millions of people against this new H1N1 flu," Andrew Cuthbertson, CSL's director of research and development, told reporters. He called swine flu "a novel strain of influenza" and said the trial would determine the dose and schedule of the vaccination, the AP reported.

As was the case when the H1N1 swine flu virus first surfaced in Mexico and then the United States in mid-April, infections in the Southern Hemisphere continue to be relatively mild, much like the seasonal flu, and recovery is fairly quick.

U.S. health officials said last Friday that development of a vaccine for the H1N1 swine flu is on track, with the first doses possibly ready by the fall.

Initial tests of a vaccine were expected to start soon, possibly within weeks, although results about its safety and effectiveness wouldn't be known for about month after that, officials said.

Secretary of Health and Human Services Kathleen Sebelius announced plans for a voluntary vaccination program in the fall, "assuming availability of a safe and effective vaccine," Dr. Anne Schuchat, director of the National Center for Immunization and Respiratory Diseases at the U.S. Centers for Disease Control and Prevention, said during a press conference.

Schuchat said the CDC is working with states and local governments to develop vaccination programs. On July 29, the CDC's advisory committee for immunization practices will meet to discuss who should receive the H1N1 vaccine. The committee also will look at who should be vaccinated first -- for example, health-care workers -- if the vaccine is in short supply.

As vaccine development continues, the H1N1 swine flu virus continues to sweep around the world.

On Friday, the CDC was reporting 40,617 confirmed cases of H1N1 infection and 263 deaths in the United States, although officials believe more than 1 million Americans have been stricken with the swine flu. The reason for the disparity: The virus continues to produce mild symptoms and patients typically recover quickly.

Schuchat said she expects to see a new outbreak of H1N1 swine flu in the United States in the fall. It will most likely start earlier than seasonal flu, she said. Seasonal flu typically surfaces in late fall.

Unlike seasonal flu, the H1N1 flu continues to pose more problems for younger people, Schuchat added. "There are a higher attack rates and hospitalizations in younger adults and children," she said.

U.S. Human Cases of H1N1 Flu Infection(As of July 17, 2009, 11 AM ET)
States and Territories* # of confirmed and probable cases Deaths
Alabama 477
Alaska 218
Arizona 762 11
Arkansas 47
California 3161 52
Colorado 155
Connecticut 1581 7
Delaware 364
Florida 2188 12
Georgia 174 1
Hawaii 722 1
Idaho 143
Illinois 3357 15
Indiana 282 1
Iowa 165
Kansas 186
Kentucky 143
Louisiana 232
Maine 133
Maryland 732 3
Massachusetts 1343 5
Michigan 515 8
Minnesota 660 3
Mississippi 219
Missouri 70 1
Montana 94
Nebraska 264 1
Nevada 406
New Hampshire 247
New Jersey 1350 14
New Mexico 232
New York 2670 57
North Carolina 395 4
North Dakota 61
Ohio 161 1
Oklahoma 176 1
Oregon 465 5
Pennsylvania 1914 8
Rhode Island 188 2
South Carolina 244
South Dakota 39
Tennessee 247 1
Texas 4975 24
Utah 966 14
Vermont 59
Virginia 319 2
Washington 636 4
Washington, D.C. 45
West Virginia 227
Wisconsin 6031 5
Wyoming 106

Territories
American Samoa 8
Guam 1
Puerto Rico 18
Virgin Islands 44
TOTAL (55)* 40,617cases 263 deaths
*includes the District of Columbia, American Samoa, Guam,
Puerto Rico and the Virgin Islands

Source: U.S. Centers for Disease Control and Prevention