In a discovery that sheds new light on the history of AIDS, scientists have found evidence that the ancestor to the virus that causes the disease has been in monkeys and apes for at least 32,000 years

Scientists said Thursday that a new AIDS vaccine, the first ever declared to protect a significant minority of humans against the disease, would be studied to answer two fundamental questions: why it worked in some people but not in others, and why those infected despite vaccination got no benefit at all.

More than six million doses of swine flu vaccine will be available by the first week in October, more that twice as many as had been recently expected, federal health officials said. As before, however, most will be the FluMist nasal spray, which is recommended only for people ages 2 to 49 and not for pregnant women or people with health problems.

Defying the expectations of experts, clinical trials are showing that the new H1N1 swine flu vaccine protects with only one dose instead of two, so the vaccine supplies now being made will go twice as far as had been predicted.

Up to 90,000 deaths from swine flu in the United States, mostly among children and young people?

Up to 1.8 million people hospitalized, with 50 percent to 100 percent of the intensive-care beds in some cities filled with swine flu patients?

Up to half the population infected by this winter?

The United States will donate 420,000 packets of the antiviral drug Tamiflu to the Pan-American Health Organization to help fight the swine flu pandemic in Latin America and the Caribbean, federal health officials said Thursday. Argentina, Brazil, Chile and other countries are experiencing rapid increases in serious cases and deaths as the winter flu season sets in.

Contrary to the popular assumption that the new swine flu pandemic arose on factory farms in Mexico, federal agriculture officials now believe that it most likely emerged in pigs in Asia, but then traveled to North America in a human.

But they emphasized that there was no way to prove their theory and only sketchy data underpinning it.

International migrant workers, foreign students and political refugees are often endangered by laws that discriminate against people with AIDS, the advocacy group Human Rights Watch reported last week.

About a third of the world

Six years of worrying about bird flu did much to prepare the United States for the current swine flu outbreak, federal officials and an independent monitoring group said Thursday, but they cautioned that there were still gaps in planning.

Researchers in Gabon and France have discovered a new species of malaria parasite, one that lives in chimpanzees but is closely related to the species most deadly to humans.

The new species was described last week in the journal PLoS Pathogens.