HIV/AIDS Vaccine

Overview

 

Vaccines have been used for over 200 years to prevent diseases like smallpox, measles and polio from spreading across populations. Vaccines are not cures, but rather treatments that can prevent disease or infection. They are the only long-term solution to controlling a viral epidemic. A vaccine, when administered to an individual, provokes an immune response in order to teach the body to recognise a particular disease-causing organism in the future. In this way the body is prepared to launch an effective attack against the particular organism, thereby preventing disease.

Currently, vaccine researchers are developing a preventative HIV vaccine that can teach the body's immune system to recognise and protect itself from HIV.

The HI virus usually attacks the important T-helper cell, which co-ordinates the immune system's response to infections. The ideal vaccine will produce antibodies that will neutralise the virus before it penetrates the immune cells, and stimulate an immune reaction inside the T-helper cell to defend itself against the virus.

At present, there is no HIV vaccine available to the public.

Challenges in Developing an HIV/AIDS Vaccine

Scientists have determined that an ideal vaccine — single dose, low-cost, long-lived, stable, safe and effective — will be difficult to develop in the short to medium term. Scientists are therefore also considering partially effective vaccines that could still save millions of lives.

Challenges:

• Generally, vaccines are developed to protect against one strain of virus. HIV is genetically unstable and has many strains. It is not yet known whether a vaccine will have to be developed against each strain (or subtype) of HIV
• HIV vaccine development is complicated by the fact that HIV infects the very cells that a vaccine triggers to produce immunity, namely the T-helper cells
• In order to develop a vaccine, scientists must first know which responses protect against which virus so that the vaccine can stimulate a specific response. However, very few people have immune systems which prevent HIV infection, or maintain low viral loads when infected. Some individuals have been found to remain HIV-negative despite multiple exposures to the virus, immune system responses that to date scientists have found difficulty in stimulating or replicating
• Because HIV can exist in the body as a free virus or inside infected cells, a vaccine will have to induce a response in both humoral (antibody) and cellular immune response mechanisms. This has not been achieved yet with any of the test vaccines that have been developed
• The current trials of vaccine candidates are nearly all based on a single hypothesis, "that a vaccine can confer protection by eliciting a cell-mediated immune response". If this hypothesis is proved wrong after the first large-scale trials (results due, at earliest, 2007), the more than 30 small-scale trials now underway will be rendered largely irrelevant (IAAVI)
• The traditional method of injecting a weakened form of the virus to produce an immune response cannot be used because HIV mutates very quickly. There is a danger that a weakened or attenuated virus could possibly become virulent, or that the weakened virus might still integrate with the host cell and expose the individual to infection

International and South African Vaccine Initiatives

There are multiple international efforts to develop an HIV vaccine. Over 60 phase I/II trials of 30 candidate vaccines have been conducted worldwide, according to the National Institutes of Health in 2000. A full database of HIV/AIDS vaccines currently being researched is accessible from the International AIDS Vaccine Initiative (IAVI) website.

A Phase III trial is currently being conducted in Thailand by developers Aventis and Vaxgen. The trial involves 16 000 participants and is the most advanced trial at this stage. A phase IIb trial by Merck is the next most advanced, with proposed trial sites in the USA, Dominican Republic, Haiti, Peru, Canada and Australia (source).

Only one potential HIV/AIDS vaccine has gone through all three trial phases but it was found to be ineffective in preventing transmission by sexual intercourse or injecting drug use (source).

The South African AIDS Vaccine Initiative (SAAVI) was established in 1999 to co-ordinate the research, development and testing of an HIV/AIDS vaccine for South Africa. SAAVI contributes to international research with its focus on HIV-1 subtype C, which is the most prevalent subtype in Southern Africa, accounting for over 90% of new infections.

According to a SAAVI press release (July, 2009) "two South African developed HIV vaccines have begun clinical testing in South Africa (Crossroads, Cape Town and at Chris Hani Baragwanath Hospital, Soweto). This follows the successful enrolment and vaccination of 12 volunteers in Boston, MA, USA".

There are also a number of Phase I clinical trials in South Africa: