Oxford Martin School

Professor Jonathan Weber, Director of Research at Imperial College's Department of Medicine, has decided to abandon his search for an HIV vaccine. After 27 years in the field, he no longer believes it to be an achievable goal. In the third of our seminars on 'Global Governance Challenges', Professor Weber explained the problems involved in designing an effective vaccine and offered his thoughts on some more promising approaches to HIV control.

To date, there has been little progress with regard to preventing the spread of HIV. While we know a lot about the cell and molecular biology of the HIV virus, neither antibody-induced vaccines, nor T-cell immunisations have shown any signs of working. A second approach, the development of vaginal microbicides, (chemicals to prevent transmission by disabling the virus before it can enter the body), has yielded disappointing results in clinical trials.

However, the quality of life of those already infected has been increasing dramatically, thanks to the spectacular success of improved antiretroviral treatments (ARVs). While ARV drugs cannot destroy HIV, they do weaken its effects. Today, many patients with HIV live relatively normal lives with near-average life expectancies. This has led Professor Weber to conclude that ARVs might be used to reduce transmission rates.

His theory draws on two observations. The first comes from a study in the Rakai district of Uganda, involving couples in which just one partner is HIV positive. It found transmission of the HIV virus to be limited in cases where the patient's body was able to spontaneously control the virus. These patients had significantly lower viral loads, (numbers of viruses in their body). So there seems to be a strong link between the levels of the HIV virus in a patient's blood and the probability of transmitting HIV to a sexual partner.

The second observation is that one effect of ARV therapy is to lower the viral load. ARVs work by interfering with the way that the HIV virus reproduces in the body. This reduces the viral load, impairing the virus' ability to damage the immune system and so keeping patients healthy. In fact highly active ARV therapy in combination with condom use has been shown to reduce transmission rates to less than 1%.

Professor Weber thinks that the most promising option for controlling HIV is therefore to prescribe ARVs in the early stages of infection, cutting transmission rates significantly by minimising viral loads in HIV positive patients. This is the theory behind his proposal to introduce population-based ARV therapy, or PopART.

The PopART approach has a number of benefits:

• Drugs are only administered to those already infected with HIV, making it easy to dispense treatment.
• There is a double benefit: the same treatment will make patients healthier while significantly reducing transmission rates.
• Approaches which mitigate the effects of HIV encourage its spread and so are often not financially sustainable solutions in poorer countries. With PopART, cumulative treatment costs will fall over time as the number of people infected with HIV drops.

There are problems of course. Clinical trials are urgently needed. Yet in order for PopART to have an impact at the population level, treatment will have to reach at least 80% of those infected. This means we need more information about how many people have HIV and who they are. But despite the challenges, Professor Weber believes PopART to be the only strategy available in 2009 with the ability to eradicate the transmission of HIV.