India has approved human volunteer trials for the country’s second preventive vaccine against HIV, the virus that leads to AIDS, health officials said on Thursday.

Home to the second-largest number of people living with the killer virus after South Africa, India started human trials on its first preventive vaccine in February and authorities say those are progressing well.

“All clearances have come for the human trials of a second vaccine,” said S.Y. Quraishi, director of the state-run National AIDS Control Organisation (NACO).

The trials on at least 30 volunteers will start in September. Scientists need to test different vaccines on the same or separate strains of a virus to develop the most effective antibodies.

A vaccine for the developing world, where antiretroviral drugs are out of reach for millions of HIV-infected people, would be the ultimate prize in the fight against AIDS. But efforts to find one have been hampered by the virus’s ability to mutate.

In February, researchers began trials on 34 healthy adult volunteers for tgAAC09 vaccine that targets HIV subtype C, widely prevalent in India, South Africa and China.

The trials for the second vaccine - called the Modified Vaccinia Ankara (MVA) - will be carried out at the Tuberculosis Research Centre in the southern city of Madras. The MVA will also target HIV subtype C.

PHASED TRIALS

Officials say in the first phase of such trials, vaccines are tested on healthy volunteers who are given a controlled dosage of the HIV subtype C virus to create resistance. All volunteers sign on to the trial, accepting the risks of possible HIV infection.

In the second phase, the vaccine is given to a small group of high-risk individuals - sex workers, drug users and homosexuals - to check for the efficacy of the dosage. They are not asked to alter their regular lifestyles.

If the vaccine is seen to work on both groups, it is given to a larger group of up to 1,000 people. All volunteers at every stage of the trial have to be HIV-negative when they sign up.

In the fourth and last phase - if the results of earlier phases are found to be satisfactory - marketing of the vaccine is done and post-marketing surveillance carried out. Experts say it takes years for a successful vaccine to be developed.

The International AIDS Vaccine Initiative (IAVI), which coordinates the global search for a vaccine, says India is important because of its advanced biomedical research facilities and strong pharmaceutical industry which has developed cheap and effective AIDS drugs that are exported across the globe.

India has an HIV/AIDS caseload of more than 5.13 million people and experts say that number could quadruple by 2010 as many people are still reluctant to discuss safe sex openly.

Many Indians cannot afford antiretroviral drugs, which cost 1,300 rupees ($29.90) a month.