Bolstering the search for HIV vaccine

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Bolstering the search for HIV vaccine

News from Thailand late last year that a vaccine trial conducted among 16 000 Thais gave a 31% protection rate against HIV infection has given scientists hope that their quest to find a vaccine to prevent HIV infection is on the horizon. But further tests are needed and South Africa is an obvious place for these to be run, given our high HIV rate.

“There was a clinical trial that was done in Thailand and the results were reported in October last year that, for the first time, showed a hint that we’ll be able to protect people from HIV by vaccination. We’re really building on those findings and there are big plans to repeat those trials, both in South Africa and elsewhere, and, of course, improve on those, but to really see whether these first signs are really something that we can use to make a better vaccine”, explained Lynn Morris, a Wits University professor and researcher for the National Institutes of Communicable Diseases (NICD), adding that “the Thai trial showed that the vaccine in question had a protective rate of 31%”.

But “that’s a very low percentage and certainly not high enough for one to implement that vaccine. It’s not good enough for use, but it’s good enough to explore further”, Morris said explaining why further studies using the Thai vaccine model will be carried out in South Africa.

“Basically, the way these trials work is that half the people get a placebo or a sugar-coated pill and the other half get the vaccine. In this case it was a huge trial. It was about 16 000 people, so roughly 8 000 in each arm. There were fewer infections in the people who got the vaccine. That’s how they calculated the 31%. And there were some indications from the vaccine trial that the protection was more effective early on. So, maybe these vaccines need boosting. That’s something that’s going to be explored, that, maybe we need to give more immunizations. We certainly need to improve on the vaccines themselves as well. But a very important thing, actually, is that it needs to be tested in different populations. The Thai population was, generally, fairly low-risk, so one of the important things is to test whether this vaccine will work in a high-risk population, and that’s why the plan is to do it here in South Africa”, she added.

Morris said the Thai study opened up a new path for the future of HIV vaccines development. For the first time scientists studied two vaccines, ALVAC and AIDSVAX, in one trial.

“In fact, it’s two different vaccines that were tested. These two vaccines were designed to stimulate two different arms of the immune response. It’s what is called a prime-boost approach. You basically prime the immune system with a particular vaccine, and, in this case it was a canary-pox based vaccine and then you boost that response with a recombinant protein.

I know that probably sounds very technical… What I want to say is the vectored vaccines, basically, are used as vehicles to get small pieces of HIV into the human body and to be taken up by the immune system and to stimulate the cells that fight infection in your body. Now that vaccine has, in fact, been tested previously and shown not to be very effective. And, then, the boost vaccine, which is a protein, has, in fact, also been tested previously and also shown not to be very effective. That vaccine is to stimulate the antibody response in your body. What is interesting about this is that we’ve basically taken two vaccines that did not show to be very promising on their own and we’ve combined them. The trick is we are stimulating both arms of the immune response. Previously, the vaccine trials tested only stimulating the antibody response or only stimulating the cellular immune response. We really do need to stimulate multiple arms of the immune response” she said.

For more than a decade scientists have been unable to come up with a successful vaccine against HIV infection. Four efficacy trials have since been conducted worldwide, with the first results being released in 2003. Scientists describe their challenge as “a moving target”. They say HIV is able to hide and change its identity, thus making it difficult to attack it. When asked if that does not mean that any attempts at finding an effective vaccine against HIV are not already doomed, Morris replied:

“I think it’s important to bear in mind that no vaccine is 100% protective, and particularly, for HIV what that means is behavior change needs to be a permanent change. People have to reduce their risk in order to avoid HIV infection. But in terms of the vaccine, whether we’re going to need to make a new vaccine to cope with this changing virus remains to be seen. Influenza is another virus that mutates a lot, and as you know with Influenza, we need to make a new vaccine every year so that the vaccine matches the virus that we’re going to be exposed to. If you take that paradigm and switch it to HIV, HIV is a far more variable virus than Influenza. It’s possible that, yes, we’re going to have to make a new vaccine on a regular basis in order to deal with that variability”.

The Thai vaccine is one of four that will be tested next year. Two others developed in South Africa will also be tested, but only to determine their safety and to see what immune responses they generate in the body. If they are shown to stimulate the right immune responses, they may well also be tested in large scale efficacy trials in the future.

Source: Health-e News , By Khopotso Bodibe

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