New Delhi, Aug. 16: India’s second candidate HIV vaccine tested in Chennai has triggered an immune response in every volunteer who received a high dose, but strengths and duration of the response need to be improved, scientists said today.

After three injections, 82 per cent of the volunteers who received a low dose and 100 per cent of those who received a high dose showed an immune response, according to scientists at the Tuberculosis Research Centre (TRC), Chennai, who conducted the trial.

The results of the phase I (safety) trial show that the vaccine has acceptable levels of safety and was well tolerated by the volunteers. The two-year trial had involved 32 healthy men and women between the ages of 18 and 50.

But this vaccine will not be pitched for phase II (efficacy) trials on its own because both the strength and the duration of the immune response can be improved, said Vadakkuppattu Ramanathan, head of clinical pathology at the TRC.

Scientists say the 100 per cent immune response with the high dose is encouraging, but whether this response translates into protection from HIV can only be determined through an efficacy trial.

The vaccine, TBC-M4, was designed by a US biotechnology firm in collaboration with Sekhar Chakrabarty, a leading Indian virologist, at the National Institute of Cholera and Enteric Diseases, Calcutta. The vaccine, based on a virus known as Modified Vaccinia Ankara (MVA), is specifically designed to work against HIV subtype-C, the predominant strain of HIV circulating in India.

“This is a milestone. Everybody who had received the vaccine showed a response, which is unusual. But we’d like to optimise and get the best possible response,” Patricia Fast, medical director with the International AIDS Vaccine Initiative (IAVI) in New York, told The Telegraph.

Ramanathan said one strategy to bolster the strength and expand the duration of the immune response would be to add a new vaccine to the MVA-based vaccine as an adjunct. “We have picked a DNA vaccine from the US as a new vaccine,” he said.

This DNA vaccine is awaiting approval from Indian health authorities. The addition of a new candidate vaccine to the MVA-based vaccine will be equivalent to testing a novel candidate — which would mean going back to Phase I (safety) tests, he said.

The MVA was the second HIV candidate vaccine to be tested in India. Earlier, the National Institute of Virology, Pune, had tested another US-made vaccine, which had not yielded an encouraging immune response. Less than 30 per cent of the volunteers who had received the vaccine displayed a response. The results had prompted the Indian government to abandon further research with the candidate tested in Pune.

The IAVI has said that it has launched work to modify the MVA-based vaccine candidate so that it is ready for large-scale manufacturing should the trial results suggest further testing is warranted.