WASHINGTON (Reuters) - A global AIDS vaccine conference this week will seek fresh strategies against the HIV virus, with experts weighing the value of basic laboratory research against large-scale human clinical trials after a string of disappointments. Approaches focusing on "neutralizing antibodies" that would allow the human immune system to block infection completely, are likely to take precedence over existing models that seek to manage infection after it occurs, experts said. "There's a real redirection and rethinking," said Lynn Morris, co-chair of a world AIDS vaccine conference that starts in Cape Town, South Africa, on Monday. "Fundamentally we don't understand enough about the human immune system and we don't know how the immune system deals with HIV." The conference -- a gathering of many of the top names in HIV research -- follows a year that saw scientists drop plans for widespread human testing of the two most promising vaccine prototypes due to safety concerns. The AIDS virus infects an estimated 33 million people globally and has killed 25 million since it was identified in the 1980s. Cocktails of drugs can control the virus but there is no cure. The two stalled vaccines, one developed by drug giant Merck and the other by U.S. government researchers, both aimed to fight AIDS by encouraging so-called cell-mediated immunity, jump-starting T-cells to tackle the virus and stop or slow the progress of HIV-related disease. But early results from a large human trial of the Merck product were discouraging and data showed the vaccine may have left some people more prone to HIV infection -- halting the tests and prompting some scientists to reconsider the model. 'A REAL SWING BACK' Morris, the head of the AIDS unit at South Africa's National Institute for Communicable Diseases, said the focus was now on another approach to fighting HIV: lab work to discover how to help the body produce antibodies to prevent infection altogether. "Neutralizing antibodies are a major component of almost all other vaccines," Morris said. "I think there is going to be a real swing back to thinking about them." The International AIDS Vaccine Initiative last month announced it was launching a $30 million joint venture research lab in California dedicated to accelerating work on neutralizing antibodies. The renewed focus on lab work has left some scientists and advocates worried that human clinical trials of vaccine candidates may suffer as funding shifts toward basic research. But Morris said limited human trials of new vaccine concepts would have to continue, arguing against some researchers who say the money would be better spent on animal research or improved AIDS drugs. "There's no guarantee that basic researchers are going to come up with the answers," Morris said. "But I feel quite strongly that clinical research should continue. If people are willing to participate in this because there is a hope that we may develop a vaccine then that's what I think we should be doing." The four-day Cape Town conference will give scientists, funders and community advocates a chance to assess the direction of AIDS vaccine research, which in 2007 accounted for about $960 million in investment -- the bulk of it from the public sector. It will also give scientists a chance to delve more deeply into the results of the failed Merck vaccine trial. Conference reports may explain how the vaccine -- made by sticking genetic pieces of HIV to a cold virus -- made some participants more likely to contract the AIDS virus, as well as hints that certain volunteers did see benefits from the Merck vaccine, keeping interest in the T-cell model alive. Morris said this year's disappointments could not be allowed to derail the pace of research. "It's an iterative process. You don't just, boom, come up with a vaccine," she said. "We have to accept that maybe it's not going to be possible. But until we know that, we have to keep trying."