US and South African scientists announce the first large-scale clinical trial of an HIV vaccine on the African continent.

US and South African scientists have announced the launch of the first large-scale clinical trial of an HIV vaccine on the African continent. 

The trial will involve around 3000 participants in five selected sites in South Africa and is expected to last up to four years. It will compare the effectiveness of the vaccine at reducing HIV infection compared to a placebo. 

Lawrence Corey, from the Fred Hutchinson Cancer Research Center in Seattle, US is one of the scientists coordinating the trial. He claims it will answer many important scientific questions for HIV vaccine development. ’This will determine the usefulness of vaccines that induce high immune response to the parts of the virus that are similar between different strains of HIV-1,’ he said.

The test vaccine, known as the MRKAd5 HIV-1 trivalent vaccine, is manufactured by US pharmaceutical giant Merck. It has already been studied for several years in Phase I and II trials involving thousands of volunteers in the Americas, Africa and Australia, where it was found to stimulate cellular immune responses against HIV in more than half of volunteers.

The test vaccine is based on an adenovirus - a common cold virus - modified so that it cannot cause a cold in humans or be transmitted from person to person. This adenovirus is the carrier or vector which transports copies of three HIV genes called gag, pol and nef. The hope is that these HIV genes will produce a cellular immune response to HIV, stimulating the body to produce killer cells that are programmed to recognise and destroy HIV-infected cells. 

The trial will be welcomed by researchers struggling to build an arsenal against the Aids epidemic. Earlier this month, late-stage trials were halted in Africa and India of a microbicide gel designed to prevent HIV infection in women. It was hoped that this would allow women to protect themselves even without the knowledge of their partner as many men refuse to wear condoms. 

The gel called Ushercell is a cellulose-based compound developed by Canadian pharmaceutical firm Polydex. It was withdrawn after women using it became infected at a higher rate that those not using it. 

Victoria Gill