By Adam Cresswellhttp://www.news.com.au/story/0,23599,22727927-2,00.html
November 09, 2007 01:00am
Article from: The Australian
AUSTRALIAN volunteers given doses of an experimental HIV vaccine have been warned they may now have an increased risk of contracting the potentially deadly virus.
Scientists involved in a global study of 3000 people yesterday revealed that a trial vaccine intended to protect against the virus that causes AIDS may in fact have made people more susceptible to HIV infection.
The failure of the vaccine - in development for more than 10 years and considered one of the best hopes of containing the spread of HIV - was described by Australian experts as "a substantial setback" with serious repercussions for future trials.
All but one of the 19 Australian participants in the trial were briefed about the findings this week.
The head of the Australian arm of the research, associate professor Tony Kelleher, told The Australian that about half of the volunteers, all in high-risk groups for HIV, were distressed to hear they might now face an increased risk of catching the virus.
About half of the 19 Australians were given the planned three doses of the vaccine, with the remainder given dummy injections.
None of the 19 has been infected with HIV and experts stress that the increased risk could be the result of chance and not the vaccine.
Alternatively, a range of other factors - such as risky behaviour, or higher circumcision rates - could explain the difference.
The so-called STEP trial, co-funded by the US National Institutes of Health, involved 3000 people worldwide at high risk of HIV infection.
It ran into trouble in September after a scheduled interim analysis of results showed the vaccine, V520, conferred no protective benefit on those who received it, compared with a control group given dummy injections.
At that point an independent group of supervising experts called for all injections in the trial to be halted.
The vaccine, made by Merck, had shown good results in earlier studies.
It used a weakened form of a common cold virus, called Adenovirus Type 5, to deliver three artificial HIV genes.
Although these genes were not able to replicate or cause HIV, the idea was that they would prime the body's immune system to recognise subsequent HIV infection and kill cells containing that virus.
Alternatively, if HIV did take hold, it was hoped the vaccine would help the immune system to better control the virus.
Analysis of the STEP data has shown that worldwide, there were 49 cases of HIV infection among the 914 male volunteers in the vaccine group, compared with 33 cases among the 922 male members in the placebo group.
The difference was more pronounced among volunteers with high prior immunity to Adenovirus Type 5.
International experts, including Professor Kelleher, were meeting yesterday in Seattle to discuss how to respond to the latest findings.
The head of immunovirology and pathogenesis at the National Centre in HIV Epidemiology and Clinical Research, Professor Kelleher said immunity to the adenovirus "varies enormously".
About two-thirds of Australians had low immunity to Adenovirus Type 5, while immunity in the Caribbean nations was much higher.
"It's not clear whether it's the adenovirus that's driving this, or something about the demographics - they have different rates of circumcision, and there's a whole lot of other differences," he said.
"We need to do some more lab testing on the genetics of the individuals involved, which will take at least three to six months.
"Among the vaccine community, (the trial outcome) is very disappointing."