India has started its first human trials of a vaccine aimed at preventing AIDS. At the same time, authorities are promising to step up efforts to slow the spread of the AIDS and HIV, the virus that causes it, which now infects more that five million Indians.

Authorities say that in the first phase of the trial, the vaccine is being administered to 30 male and female volunteers in the western city of Pune.

N.K. Ganguly heads the Indian Council of Medical Research, which is conducting the trials in partnership with the International AIDS Vaccine Initiative from New York. Mr. Ganguly says the first phase of the experiments will last about two years, but a successful vaccine may still be a decade away.

"This is one thing which is like a marathon," he said. "Around eight to 10 years it takes a product to be launched, but it all depends on how fast we get results."

The vaccine being tested in Pune is aimed at fighting the strain most commonly found in India. Human trials of vaccines against different strains of HIV, the virus that causes AIDS, are being conducted in several countries. But scientists say the ability of the virus to mutate has hampered the discovery of a successful vaccine.

India's Health Minister Anbumani Ramadoss has expressed hope that the vaccine project will be successful. But he says that "85 percent of the country's focus is still going to be on prevention."

Voluntary groups agree that halting the spread of the disease remains a critical challenge for India, where the disease now affects more than five million people.

I.S. Gilada heads one of India's leading groups working with AIDS patients. He warns the number of infected people could grow five times over the coming decade.

"If you look at the speed with which the virus is spreading, we are not able to counter with the same speed through prevention as well as through management," said Mr. Gilada. "The dynamics of the infection are very big, it may become 20 to 25 million if we do not take effective measures."

Health experts have repeatedly warned that the government underestimates the size of the AIDS epidemic in India because official figures leave out a vast number of people who carry the virus without knowing or reporting it.

An estimated two-thirds of the victims live in rural areas where health facilities are poor.

After first appearing in high-risk groups such as sex workers and drug users, the virus has spilled into the general population.