Successful Thai vaccine may be tested in SA

Further research on the world's only vaccine to show some protection against HIV may be conducted in South Africa.

This was revealed yesterday at the International AIDS Vaccine conference by Colonel Nelson Michael from the US Military HIV Research Programme, one of the lead investigators in the Thailand trial.

"There is a lot of interest in contemplating a further study in South Africa, given the robust nature of the South African scientific community and the good infrastructure," Michael told a press conference.

South Africa is also an ideal trial site given the high level of HIV risk in the country, where over 10 percent of people over the age of two are living with HIV in comparison to just one percent of Thais.

Since the announcement three weeks ago that the Thailand trial had shown a modest 30 percent protection against HIV infection, the researchers have faced criticism from their peers.

Some claimed that the results were not statistically significant enough while others criticised the fact that the trial was conducted among people facing low to moderate risk of HIV infection instead of high risk.

The trial was the biggest AIDS vaccine trial ever conducted in the world, involving 16,400 Thai volunteers aged between 18 and 30 years. Half were given the vaccine and the other half a placebo.

They were all followed for three years, and 51 of those who got the vaccine became infected with HIV while 74 of those in the placebo arm got HIV.

"This showed a modest protection of 31,2 percent," Dr Supachai Resks-Ngarm from the Thailand Ministry of Health told the Paris meeting yesterday.

Resks-Ngarm added that there were no differences in terms of gender, age, marital status or same-sex relationships between volunteers in the two arms of the trial that could have influenced the different infection rates.

"We are encouraged by the result and need to conduct further research to see why it was effective and how to use information to develop the vaccine field further," said Resks-Ngarm.

Vaccines work by teaching a person's immune systems to recognise and destroy disease-causing pathogens (eg. viruses, bacteria or fungi).

They usually contain some harmless part of the pathogen being targeted to prime the immune system to develop antibodies against it so that when it is attacked by the real pathogen, it already has the weapons to fight it.

The Thai trial was unusual in that it combined two vaccines: one called Alvac that aimed to prime the immune system to recognise the types of HIV most common in Thailand (clades E and B), and the other called AIDSVAX that boosted the body's immune system to fight infection. Both vaccines had been tried by themselves and shown not to affect HIV infection.

"This is the first evidence that the prime-boost HIV vaccine regimen may prevent infection and represents a significant step forward for vaccine research," said Colonel Michael.

Before the trial had even began, 24 eminent scientists wrote to the prestigious "Science" magazine and said that it should not be run as it involved two failed vaccines.

Yesterday, the New England Journal of Medicine (NEJM) published the results to coincide with the conference.

NEJM editor Rachael Dolin pointed out that two vaccine candidates that had failed recently had been tested on high risk groups: men who have sex with men and intravenous drug users.

"Perhaps the requirements for protection against [HIV] transmission in low-risk heterosexual persons are considerably different or less stringent than those in high-risk subject," cautioned Dolin.

Should further research on the vaccine be carried out in South Africa, however, it would have to be modified to contain Clade C, the strain of HIV most common in this country.

Conference delegates generally welcomed the results, describing them as "historic".

Harvard University's Professor Dan Barouch said the vaccines had a "small but real effect on HIV infection".

"While the effect is by no means big enough to have a public health benefit, it gives us scientific insight into where the field should go now," said Barouch.

Kerry Cullinan, Health-e News 21.10.2009