India, home to the world’s second-largest HIV population after South Africa, began its first-ever human trials of a new vaccine against the deadly virus Monday, the health minister said.

A vaccine - the best hope for the developing world where drugs remain out of reach for millions - is considered the Holy Grail in the battle against the AIDS epidemic, but efforts to find one have been hampered by HIV’s uncanny ability to mutate.

Human trials of vaccines against different strains of the virus are already being conducted in the United States, Europe, Africa and South America.

“We’ve started the first phase of clinical trials, but 85 percent of our focus is still going to be on prevention,” Anbumani Ramadoss told a news conference. “Developing a vaccine to prevent AIDS is one of the most difficult scientific challenges of our time. It is also one of the most urgent health needs.”

India has more than 5.1 million people living with HIV/AIDS and experts say the number could quadruple by 2010. The World Bank has warned the disease would become the single largest cause of death in the world’s second-most populous country unless there is progress on prevention.

The first phase of human trials in India is being conducted on 34 adult volunteers at the government-run National AIDS Research Institute in the western city of Pune along with the International Aids Vaccine Initiative, health department officials said.

The trial is aimed at fighting the strain C, the subtype most commonly found in the country.

Indian health officials said the first phase of trials would take about two years and it would be at least eight to 10 years before a vaccine could finally be developed.

“This is a marathon, and not a sprint,” said Seth Berkley, head of the International Aids Vaccine Initiative.

India’s HIV problem has assumed serious proportions despite health programs to halt its spread. Over the years, HIV/AIDS has moved beyond traditionally high-risk groups such as homosexuals, commercial sex workers and drug users.

The virus is spreading into families, infecting mothers and children, and many people do not even know they are infected because of the widespread lack of awareness about the disease.

Experts say the most alarming trend is the spread of the disease to villages, with rural India accounting for 59 percent of infections compared with 41 percent in cities.