More than 25 years into the Aids pandemic, scientists finally have a vaccine that protects some people -- but instead of celebrating, they are going back to the drawing board.
The vaccine, a combination of two older vaccines, only lowered the infection rate by about a third after three years among 16 000 ordinary Thai volunteers. Vaccines need to be at least 50% effective, and usually 70 to 80% effective, to be useful.
Worse, no one knows why it worked.
"Additional studies are clearly needed to understand how this vaccine regimen reduced the risk of HIV infection," said Dr Eric Schoomaker, surgeon general of the US Army, which helped pay for the study.
Dr Anthony Fauci, director of the US National Institute of Allergy and Infectious Diseases, said, "We need to bring the best minds together and map the way forward."
Aids vaccine ‘risky business’
The vaccine is a combination of Sanofi-Pasteur's ALVAC canarypox/HIV vaccine, which includes synthetic versions of three HIV genes, and the failed HIV vaccine AIDSVAX, made by a San Francisco company called VaxGen and now owned by the non-profit Global Solutions for Infectious Diseases.
"It is likely that significant efforts will be needed to fully understand the study results and to appreciate how they will inform the next steps to develop and deliver a safe and effective HIV vaccine," Dr Peter Kim, president of Merck Research Laboratories, said in a statement.
Merck's first Aids vaccine failed in 2007. "I am not sure this will encourage companies to immediately jump in," said Mitchell Warren of the non-profit Aids Vaccine Advocacy Coalition.
"What we hear from pharma and from small biotechs is that they are fascinated by an Aids vaccine but as a business proposition, it is too risky."
The Thai trial may help them re-evaluate, Warren said. But first, some scientific direction is necessary.
"What is needed there is more in-depth analysis, to extend these findings, doing both clinical (human) and preclinical (animal) studies to find out why it is working and how we can make it better," said Jim Tartaglia, vice president of research and development at Sanofi.
Vaccine the ‘only way to conquer it’
Companies and non-profits along with governments have been working to make a vaccine against the human immunodeficiency virus that causes Aids. The fatal and incurable virus has killed 25 million people and infects 33 million now.
Experts agree that a vaccine is the only way to conquer it, but the virus mutates unbelievably fast, can hide from the immune system and attacks the very cells sent to battle it.
To work, any HIV vaccine would have to activate both arms of the immune system -- the antibodies that home in on invaders such as viruses to neutralise them, and the T-cells that recognise and destroy viruses.
This vaccine did not appear to generate much of either response, and yet prevented infection 30% of the time.
Even more confusing, among the 51 people who were vaccinated but were infected anyway, the virus thrived just as well as it did among unvaccinated HIV patients. Researchers would not have expected that -- they would have expected the vaccine to at least make the infection less serious, as influenza vaccines do, for example.
Fauci wonders if the vaccines stimulated some component of the immune system that has been overlooked.
Vaccine rewards ‘substantial’
Dr Donald Francis, a former government vaccine expert who helped develop AIDSVAX and who helped found Global Solutions for Infectious Diseases, said his team would be developing smaller studies to answer some of these questions. "We have a limited amount of vaccine now," Francis said.
The findings do offer renewed hope for finding a better vaccine. "There are now six approaches that look better than Merck's vaccine in the best of the animal models," said Dr Seth Berkley, head of the International Aids Vaccine Initiative, which funds studies.
IAVI believes the rewards could be substantial -- not just stopping the worst pandemic of our times, but financially. "At its peak, an HIV vaccine could represent 5% to 13% of the total global vaccine market," IAVI estimates.
At $2 a dose for the developing world and $100 in richer countries, IAVI estimated companies might bring in $1.6 billion to $3.8 billion a year with an HIV vaccine.
Yet the private sector accounts for just 10% of all Aids vaccine research and development funding, the group estimates. – (Reuters Health, September 2009)
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