The two last days were filled with news about the latest large scale vaccine trials against HIV. Here’s a simple Q&A
What was the news ?
The news was that the latest HIV large scale trial of a vaccine showed that the vaccinated group had a reduced rate of 31% of infection versus the control group. The trial took place in Thailand.
What vaccine was this ?
The trial used two vaccines (ALVACR HIV and AIDSVAXR B/E) that were matched to the strain of HIV that is predominant in Thailand (Clade E). The study had hypothesized that the vaccine would reduce HIV acquisition by 50 percent. The study results were statistically significant, although they did not reach the level that had been specified as the rate of infection was reduced by 31%.
How large was the trial?
This is a big study with 16,000 adults enrolled since 2003. Budget was solid too as the US government put up 105 million dollars for the study.
The study recruited adults in the community in two provinces of Thailand with high HIV prevalence (Chon Buri and Rayong), but did not specifically target individuals at high risk of HIV infection. Volunteers for the study were adults aged 18-30. It was a randomized trial, matched for sex, behavior, age.
Out of the 16,000 adults, half got the vaccine and half got the placebo. The study started in 2003 the Volunteers were tested for AIDS for 3 years. The results were only ready just 3 weeks ago (beginning of September 09)
What should we make of the success ?
First it should be understood that the result was a surprise. After all the two strands of vaccine used were both proved to be inefficient.
The effect is modest but it’s a stepping stone. It open up doors to identify what the exact mechanisms of this protection is. Scientists now will have to identify what has protected these people in order to try to amplify that effect in future test.
Is it ethical to conduct HIV tests on people that will practice unprotected sex ? Isn’t it better to teach them to have protected sex?
Actually, in vaccine trials huge as these, all participants and everyone who gets the vaccine are intensively counseled on how to avoid being infected. It makes the vaccine trial more difficult but training is a very important part of the aid program. The training is conducted by special counselors completely dissociated from the scientists.
Why is it so hard to make a vaccine against HIV?
The virus has been discovered in 1981. It has been in the history of science the most challenging virus to tackle because of its specificity:
a) The immune response of the body is far less than for any other virus, it has been branded ‘inadequate’. Only about 2% of infected people have developed natural immunity read here
b) The ability of HIV to establish latency, allowing it to “hide” in host cells and elude immune surveillance
c) The extraordinary diversity and mutability of the virus; the capacity of the virus to avoid a protective immune response by masking more conserved components of the virus; and the ability of HIV to destroy or cause the dysfunction of critical immune system cells.
There are several other vaccine candidates in the research pipeline and today’s encouraging results will provide renewed enthusiasm for human clinical trials, as well as additional HIV vaccine discovery.
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