HIV/AIDS - A race against time

Izelle Theunissen, MRC News

With HIV/AIDS infection rates showing no signs of abating, the urgency for a preventive vaccine has never been greater. Dr Tim Tucker, recently appointed head of the South African AIDS Vaccine Initiative (SAAVI), shares some thoughts on the vaccine trials and the road ahead. "We believe that the only way to eradicate HIV/AIDS or to dramatically reduce the number of infections is by making a good HIV vaccine." Speaking is Dr Tim Tucker, who recently took over from Dr Walter Prozesky as head of SAAVI.

This initiative was launched in 1999 and was tasked by Government to co-ordinate the South African effort aimed at finding a safe and affordable vaccine against HIV/AIDS within 10 years. The entire Southern African region is set to benefit from a successful vaccine, because the SAAVI initiative is constructing a vaccine based on the clade C strain of HIV that is circulating in the geographical region. Should South Africa manage to accomplish this feat, it would have been done in less than half the time usually needed for developing a conventional vaccine. 

"I'm very optimistic – we've got history on our side," Tucker says, referring to the polio and smallpox epidemics which also claimed millions of lives before vaccines were developed.

Tucker is a medical doctor and clinical virologist who previously researched new medications against liver diseases at the University of Cape Town's Medical School at Groote Schuur Hospital. He sees his new appointment as a challenge, co-ordinating the effort that involves many teams of people across the country tackling various aspects of vaccine developing and testing.

"We have groups at the Universities of Cape Town and Stellenbosch that are designing the new potential vaccines, and other groups dedicated to the field testing. We also have the laboratory at the National Institute of Virology in Johannesburg that is going to test the immune functions of those that are going to be vaccinated. Then there's a group at the University of Natal that is developing ethical protocols for the testing procedure. Another group, SA HIVAC, which is based at the MRC, is a consortium of groups which will develop a legal framework for AIDS vaccines as well as ensure adequate media contact and training. They will also develop community awareness and lobby politicians. So it's really a very extensive national and international network," he explains. 

The testing procedure 

The testing procedure for any vaccine or medication is no quick-fix operation. "All new medications have to go through three phases of testing. The phase I clinical trials involve between 20 and 50 people and will test the safety of the vaccine. Once we've established the safety of the vaccine, we'll move on to the phase II trials. Here we will test the different doses and routes of administration to establish what is the best way to use the vaccine. Once this has been successfully done, we'll move on to a phase III efficacy study. During this, the vaccine is administered to thousands of volunteers in the field, to see if it actually protects people against the virus," Tucker says.

While the phase I testing will take between a year to 18 months to complete, Tucker is quick to warn that the public should not expect vaccines in the clinics during the next few years. "It's a long-term programme and I think the earliest we can expect vaccines in the clinics is in about ten years' time," he says.

Success and seropositivity 

But how will scientists determine whether the vaccine is successful? According to Tucker, a vaccine is successful if it produces an immune response. This means that your body reacts by producing antibodies and ‘killer cells' against the harmless parts of the virus that is in the vaccine.  He stresses the safety aspect of the vaccine. "Nobody who ever takes part in any HIV vaccine clinical trial will become HIV-positive because of that vaccine. There is no live virus in any of the vaccines and so nobody will ever become HIV-positive," he says.

When you become infected with the ‘real' HIV, you also produce antibodies and it is by routine testing for these antibodies that it can be determined if somebody is indeed HIV-positive. So how would scientists determine during the phase III trials whether a person has become HIV-infected or merely, because of a successful vaccine, HIV antibody-positive?

"We have tests readily available that can determine between those who have been vaccinated and those that have been infected by HIV. And each person who is given the vaccine will be protected by law to make sure that they're not prejudiced if they become antibody-positive because of the vaccine," Tucker explains.

Trial participants will also be fully counselled to keep to all of the normal safety precautions such as using condoms and avoiding multiple sex partners. "We don't know at this stage whether our vaccines are going to be successful, and even if they are, there are very good reasons to continue support such as condom distribution and treating sexually transmitted diseases," he says. 

Collaboration 

With more efforts to find a successful vaccine against HIV progressing in other parts of the world, the South African effort is recognised internationally. Prof. Carolyn Williamson, who leads the UCT-based group constructing the VEE vaccine, recently shared a World Technology Forum Award, with her collaborator from Alphavax, Prof. Bob Johnson, for the development of the vaccine. This VEE vaccine will be tested in Durban and Soweto next year. The HIV genes characterised by this group are being used in three other vaccine efforts around the world. So collaboration is definitely the name of the game.

Tucker is quietly confident about the team's success. "We don't have an adequate treatment for HIV – those treatments that are available are costly, don't cure and merely slow down the progression of the disease. So what we're trying to do is find a vaccine that will either prevent infection or prevent the disease associated with infection. Whether we can do it or not, time will tell, but we're very optimistic." For more information, contact Dr Tucker at tel.: (021) 938-0262 or e-mail: tim.tucker@mrc.ac.za

 

December 2001