BEIJING -- The answer to a crucial question about the vaccine for the advancing swine flu -- one shot or two? -- may be near.

Chinese officials say they are about to approve vaccines that prevent the new flu in a single dose.

If they're right, it would be good news. Many health researchers fear it will take two shots to protect people, vastly complicating efforts to stem the spread of the illness.

The World Health Organization says it is encouraged after reviewing the test details from one of the two Chinese vaccines. However, experts said more results are needed from other vaccine makers to determine if one dose would be potent enough.

Australia-based CSL should know within days whether one dose of its vaccine, administered to volunteers in that country in late July, was enough. CSL to date has been mum.

In about two weeks, the U.S. expects to announce initial test results from its vaccine, which is the same type as one of the Chinese versions, said Dr. Anthony Fauci of the U.S. National Institutes of Health.

"From what I've seen and heard of the data, it looks encouraging," Fauci said of the clinical trials of the Chinese vaccine from Sinovac Biotech Ltd. "This is very good news. Let's hope the material that we're using has similar results."

Most experts agreed.

"Everybody is desperately hoping that one (shot) will do because then that's much easier to administer," said Jodie McVernon, a vaccine expert at the University of Melbourne who is involved in Australian trials of swine flu vaccines for young children. She had not seen the Chinese trial results.

However, James McGlothlin, a member of Purdue University's pandemic planning committee, was cautious about the Chinese report. "They've got some very good scientists over there, but anything that sounds too good to be true ought to be scrutinized," he said in a telephone interview.

"I'd like to look at some of the clinical trials," that led to the one-dose conclusion, he said. "In China, the rules are a little bit different in terms of human subjects," and it's not clear what safety factors were in place, he said.

China's State Food and Drug Administration said on its Web site it will make a decision this week on approving the two vaccines, which completed testing last month and passed reviews by panels of about 40 experts. Four other vaccines are being reviewed, it said.

Government-backed vaccine makers Sinovac and Hualan Biological Engineering Inc. said their studies show one shot is effective on people ages 3 to 60. More than 3,000 people participated in the trials.

Should China export vaccines, however, quality concerns could arise. Though China is a worldwide manufacturing center for pharmaceuticals, suppliers have been known to substitute cheaper and sometimes lethal ingredients. Tainted cough syrup was linked to several deaths in Central America and blood thinners made with contaminated products are suspected in dozens of deaths in the U.S. in recent years.