He showed an obvious passion for his work, which, in his own words, has won him many 'credits' and also 'responsibilities'.

Dr Ho gained international renown after he was named Time magazine's 1996 'Man of the Year' for his invention the now-famous 'cocktail therapy', or combination drug treatment, for Aids patients. Time said it named Dr Ho 'for helping lift a death sentence, for a few years at least, and perhaps longer' for Aids patients. He was also awarded a US Presidential Medal in 2001.

The director of the Aaron Diamond Aids Research Centre at the Rockefeller University in New York has since been regarded as the world authority on Aids research.

A few years ago, he switched his research focus from drugs to vaccines. He also spent more time outside the laboratory to promote public health in developing countries on the African continent and also in China.

'We know that drugs are helpful. But so far, they haven't changed the epidemic. While drugs have been quite useful since 1996, the epidemic continues to grow. Much of the epidemic in China has occurred in the presence of having good drugs available in the world,' he said.

'But the penetration of these drugs is not good. We want to work on an agenda that can help the developing world to stop the spread of HIV.'

Just a few figures are enough to illustrate the devastation caused by the epidemic. At present, about 42 million people are living with HIV. Another 25 million have been killed by the disease since it was identified in 1983.

Research on Aids vaccines is a race against time. Dr Ho said there were now half a dozen 'vaccine candidates', but nothing had been proven yet.

His team's research in two vaccines has made some progress. A DNA vaccine contains five HIV genes that are used to stimulate the body's immune system. A clinical trial in humans was launched in November last year, with 45 volunteers. The clinical trial of another vaccine, called MVA (modified vaccinia ankara), on humans is expected to start in November, with 48 volunteers. The centre is waiting for approval from the US Food and Drugs Administration.

Dr Ho said it would take at least another five to 10 years for an Aids vaccine - if an effective candidate could be proven - to be administered to patients in any large-scale programme.

'Implementation [of a vaccination programme] worldwide is very difficult. Even though we have a vaccine that's completely protective against polio, for example, we still have polio today.'

While developing countries suffer the most from HIV, sadly, patients there have the least access to effective treatment. Dr Ho said this 'inequality' made controlling the epidemic very difficult.

'Treating patients in developing countries has become an important priority. The only way is for rich countries to provide the funding to buy medicine and help the developing countries.'

He said pharmaceutical companies should also 'make the right balance' between profit-making and carrying out their social responsibilities.

He said he understood that drug manufacturers had invested billions of dollars in research and development, and there was nothing morally wrong for them to make profits, 'however, they should principally make their profits in the developed countries'.

Stepping out of the laboratory and into the frontline of the Aids battle has become another new direction for Dr Ho.

After visiting the 'Aids villages' in Henan - where local residents were infected with HIV through selling blood - he realised that a high-level advocacy campaign was urgently needed to raise people's awareness about Aids.

He set up the China Aids Initiatives, a network of local medical institutes, government departments and overseas Aids organisations, to promote prevention and care programmes on the mainland.

The Chinese ministry of health officially recorded 30,736 HIV infections by the end of 2001. However, both the central government and the United Nations body, UNAids, estimated the actual number could be one million. According to UNAids, the figure will jump to 10 million by 2010 if nothing is done to curb the epidemic.

Dr Ho decided to dedicate his career to HIV after seeing some of the first HIV cases when he was a young doctor in 1981 in the US.

'People were dying and I was moved by that. In the beginning, there was lots of discrimination and lots of suffering. I have seen the situation improve so much in the US. Then I went to Africa, China and see the same kinds of problems all over again.'

In most places he travels to on the mainland, people recognise him and see him as their hope. 'When I go to China, there will be some patients grabbing my hand and they won't let go - they will kneel down and say 'please help'. They may not know the details of what I've done. They know that I work on this and may have some solutions. Because of these types of experiences, I know I have to devote my time to this.'

Dr Ho said his work in China also completed two 'full circles' in his life.

'I was a physician before I was a scientist, and now this public health role brings me back to that position somewhat. For me, on the personal level, I left Taiwan when I was young, and pretty much have spent most of my life in America. But now to be able to come back to this part of the world to contribute something on public health for China is another full circle.'

He said it was a sense of responsibility - that came with the credits to his career - that kept him engaged in the fight against the virus. 'Being a Chinese, I want to make sure I contribute to [fighting] the Aids problem in China. But it is more than that. There is also a social responsibility, especially when you have been given a lot of credit. I can give back to the subject I know the most.'

Dr Ho said the Sars outbreak had had a 'huge impact' on the central government in terms of controlling infectious diseases. 'Sars was a loud wake-up call for China. It taught China the importance of controlling epidemic diseases. It revealed deficiencies in the system.'

He said the central government had improved the system after Sars, and now it needed to further improve to address HIV. 'HIV may not be as dramatic as Sars was. But in the long run, it is the bigger problem. HIV is so slow, but Sars is acute and more dramatic. But HIV kills more people in a couple of hours than Sars did in a whole year.'

He said what he has witnessed in Henan was a painful experience that he could never forget.

'The land is rich but the people are poor. It is poverty that led those poor farmers to sell blood and be taken advantage of. People took a short cut in the blood collection and allowed infections to occur in such a tragic way.

'Human life means so little there. But that has to change. Just because you have 1.3 billion people does not mean human life is any less valuable.'

He said patience and a 'not-too-critical manner' was essential in working with the central government. 'If you constantly criticise your partner, that is not much of a partnership. That is the way in business, in social relations - why should working with a government be any different?'

Dr Ho also has a close relationship with Hong Kong. In 2002, he was headhunted by University of Hong Kong council chairman Victor Fung Kwok-king to run the city's top academic institution. But he turned down the offer.

'My first aim is still to continue to work on HIV/Aids. If I had taken that position, I would have had to give up the Aids agenda.'

Last year, his centre and the university set up a joint Aids research laboratory in Hong Kong.

Asked about the future target of his career, he smiled and said: 'I am already 51 and the vaccine research will occupy my time for many years. I am not sure if there would be much career thereafter.'