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Optimism despite HIV vaccine failure

Optimism despite HIV vaccine failure

Wed, 21 Nov 2007
Despite the recent failure of an HIV vaccine trial, the scientific community remains optimistic, a researcher said in Johannesburg on Tuesday.

Merck's STEP trial had been "our best shot", said head of the Aids virus research unit at the National Institute for Communicable Diseases, Professor Lynn Morris.

"To give up now would be a big mistake. A solution is not around the corner, it won't be a magic bullet, it will be part of a prevention package."

More basic research needed

Speaking at a public lecture on the possibility of finding an HIV vaccine, she said there was a need for more basic research on the HIV virus itself.

Morris said the STEP trial, which was halted first in USA, then in South Africa, was a "well-run trial that gave us answers".

"At the very least we'll find out why it didn't work."

Morris reminded her audience that it took almost 47 years to develop a polio vaccine. Efforts to do so were almost abandoned.

Morris said the STEP trial, which was started in 2004, was abandoned on 18 September this year because it neither slowed nor reduced infections. There was also the possibility that people exposed to the vaccine developed increased susceptibility to HIV infection.

STEP involved 3000 volunteers, mostly in the USA, and two-thirds of whom were gay men at high risk of contracting HIV due to their behaviour.

During the course of the test 33 of 889 volunteers (3.6 percent) who were given the placebo, became infected with HIV, due to their high-risk behaviour. Of those given the vaccine, 49 out of 905 (5.4 percent) contracted HIV.

STEP's sister trial in South Africa — Phambili — was abandoned on 15 November.

"Ethically you have to stop the trial if futility (ineffectiveness of a vaccine) is shown in another trial."

The STEP trial was based on the use of cytotoxic T-cells (CTL). CTL killed virus-infected cells, but only after the virus had been integrated into the body's DNA. The HI-Virus however became dormant, so CTL could not kill it.

"After a number of years the virus escapes the CTL response."

Morris said all previous strategies used to develop other vaccines had proven ineffective against HIV.

The HI-Virus inserted itself into the body's genetic material, becoming an integral part of it. It targeted CD4 cells, which orchestrate the body's immune response.

"It destroys the very cells we are trying to stimulate [into an immune response], said Morris.

HIV a moving target

HIV was also difficult to eradicate as it was a "moving target", showing an unprecedented level of genetic diversity. A vaccine would need to protect against a wide variety of its forms, she said.

Most vaccines, for all diseases, were between 70 and 95 percent effective. A vaccine stimulates an immune response to create resistance to infection.

Morris said a vaccine was needed because, since the emergence of Aids in the 1980s, there had been a "relentless increase" in the number of infections. This was despite antiretroviral therapy.

"For every one person on treatment, another six become infected. It's a losing battle."

More than 15 percent of adults are estimated to be HIV-infected in southern Africa. Ten percent of all HIV infections were in South Africa, said Morris.

Morris advocated a multi-pronged approach to combating Aids. This involved male circumcision, which had been shown to reduce HIV infection, as well as microbicides for women.

She said a closer look also had to be taken at the immune systems of "elite controllers" — people who had been living with the HI-Virus for over 20 years without the help of antiretrovirals

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