New Delhi, April 11: India may consider a new strategy to evaluate vaccines against HIV after the first trial of a candidate vaccine in India did not yield expected results, senior scientists have said.

The highest dose of the candidate vaccine tested by the National AIDS Research Institute (Nari), Pune, could generate an immune response in only 25 per cent of the volunteers, the researchers said.

“I would describe these results as less than expected,” Sanjay Mehendale, a principal investigator at Nari, told The Telegraph.

But the results, he said, suggest that the candidate vaccine may be worth pursuing in a different strategy that involves sequential delivery of multiple candidate vaccines — what scientists call a prime-boost approach.

In the prime-boost strategy, the first vaccine sensitises, or prepares, the body’s immune system, while the second vaccine boosts the immune response. Scientists are now debating which candidate vaccines to combine for such a strategy in India, Mehendale said.

The trial at Nari was part of a three-country study in which different doses of a candidate vaccine based on a virus called adeno-associated virus (AAV) were given to volunteers in Belgium, Germany and India.

Thirty men and women between the ages of 18 and 50 participated in the Pune trial designed to evaluate the safety of the candidate vaccine and to study the immune response it produces in humans. The vaccine was evaluated in three different doses — one billion, ten billion and a hundred billion viral particles.

The results, presented at a scientific conference in Los Angeles earlier this year, have shown the vaccine is safe at all the tested doses. However, even at the highest dose of 100 billion viral particles, only 25 per cent of volunteers displayed an immune response.

“It’s possible that higher doses and multiple doses of the vaccine may lead to an even better response,” said Jean Louis Excler, senior medical director with the International AIDS Vaccine Initiative in New Delhi.

An even higher dose of this vaccine — containing one trillion particles — is now under evaluation in Africa, Excler said.

Scientists said the results were not surprising. Several candidate vaccines that had generated a very good immune response in animals have not produced the same response in humans, a senior virologist said.

Some 30 vaccine candidates are under trials in 19 countries, but only one is in large-scale efficacy trials in Thailand .

“The vaccine could still be considered for study in a prime-boost strategy in which two vaccines are given after a short gap of weeks to months,” said Shahid Jameel, head of virology at the International Centre for Genetic Engineering and Biotechnology in New Delhi.

The results of the trial of a second candidate vaccine under way in India at the Tuberculosis Research Centre in Chennai are expected only by next February, but preliminary results appear “encouraging”, Excler said.