New Delhi, Nov. 19: The discovery that a virus used in experimental HIV vaccines damages the immune system of mice is indicative of a race for a vaccine despite vexing knowledge gaps in biology, scientists said.

As reported in The Telegraph today, researchers at The Wistar Institute in Philadelphia have shown through a study on mice that the virus weakens the ability of the immune system to kill HIV-infected cells.

Candidate HIV vaccines based on the adeno-associated virus (AAV) have been tested in volunteers over the past two years in India, Belgium, Germany and South Africa. The Wistar team had cautioned its findings implied that AAV-based vaccines might increase the vaccine recipients’ susceptibility to progress more rapidly to AIDS -- if they get infected with HIV.

The Wistar findings and independent trouble with a different HIV candidate vaccine earlier this year have prompted scientists to point out that vaccine tests are proceeding amid poor knowledge of the human immune system.

“The vaccine effort is certainly well-intentioned. But in desperation to find a safe and effective vaccine, they might be rushing into trials,” said Hildegund Ertl, the Wistar Institute scientist who led the study.

Earlier this year, a medical board stopped an international trial of a candidate HIV vaccine called the STEP trial that had enrolled more than 3,700 volunteers in several countries, including Australia, Brazil, Canada, the US and South Africa. The vaccine neither prevented HIV infection, nor influenced the course of the infection in people who became infected.

Instead, more people who had received the candidate STEP vaccine became infected with HIV than people who had received a placebo -- a sham vaccine.

But scientists spearheading the vaccine effort said the world did not have the luxury to wait for a full understanding of the immune system. “History tells us that it takes a long time to develop a vaccine,” said Seth Berkeley, the president of the International AIDS Vaccine Initiative, a global non-profit organisation working towards a safe and effective vaccine.

It took 47 years after the polio virus was discovered before a vaccine was developed. Chicken pox took 42 years, rotavirus which causes diarrhoea, took 33 years, Berkeley said. It is only 24 years since the discovery of HIV.

About 39 million people are infected with HIV which kills three million each year worldwide. Anti-HIV drug therapy can prolong the lives of people who are infected, but it is not a cure. The UNAIDS has estimated that providing prevention, treatment and care to all who need in the developing countries would cost a staggering $45 billion by 2015.

“Only a vaccine holds out the hope of eliminating AIDS,” Berkeley said in a statement issued in response to the termination of the STEP trial.

Scientists said gaps in knowledge about how the human immune system interacts with HIV were frustrating. “The exact immunological mechanisms required to effectively protect humans from this virus are still unclear,” said Udaykumar Ranga, a scientist at the Jawaharlal Nehru Centre for Advanced Scientific Research in Bangalore.

But scientists pointed out that mechanisms of some successful vaccines remained unknown. “The small pox vaccine helped us eradicate a terrible disease. But how it worked is still not completely understood,” Ranga told The Telegraph.

The response of the immune system to the ability of HIV to mutate rapidly is another unresolved issue. “HIV replication is highly error prone. Every round of HIV proliferation has progeny that differ from parents and from each other,” said Satyajit Rath, a senior scientist at the National Institute of Immunology, New Delhi.

A rapidly mutating virus makes vaccine design difficult. But immune protection from HIV is believed possible because some people never contract the virus despite repeated exposure, while others are infected, but do not develop AIDS.

“The vaccine effort right now is informed through knowledge, but it is empirical knowledge. It’s an area where mechanisms are not properly understood,” Rath said.

“Empiric research, informed by the best scientific understanding of the time, is the only way forward at this time,” said Patricia Fast, the director of medical affairs with the AIDS Vaccine Initiative.