Nairobi, Kenya ? A quarter-century after AIDS was first identified, there is mounting evidence to suggest that the spread of HIV, the virus that causes AIDS, is at last slowing down.

The number of new HIV infections has fallen in most of sub-Saharan Africa and may be leveling off in India, regions that together account for more than three-quarters of the world’s estimated 40.3 million HIV-infected people.

HIV isn’t spreading in India and China as fast as experts feared just a few years ago. And in some regions, such as East Africa, there’s evidence that people are having safer sex, slowing the spread of the virus.

This doesn’t mean that the AIDS crisis is over. The total number of people living with HIV continues to rise at an alarming rate, even if more slowly than before. The disease is overwhelming impoverished countries, and life-prolonging drugs remain out of reach for the vast majority of sufferers.

But many specialists now believe that in wide swaths of the world the explosion of new HIV infections is coming to an end, though they say it’s still much too early to let down their guard.

“In all likelihood, new HIV infections have peaked globally,” concluded a recent commentary in the British medical journal The Lancet. The commentary’s authors were James D. Shelton and Daniel T. Halperin of the U.S. Agency for International Development and David Wilson of the World Bank.

Experts don’t know precisely why HIV infection rates are slowing.