Aug. 15 (Bloomberg) -- An AIDS vaccine is 5 to 10 years away from discovery because scientists haven't solved a basic scientific riddle: How to prevent the deadly virus from invading cells that make up the body's disease-fighting immune system.

More than 30 experimental vaccines are in testing against HIV, the virus that causes the disease, according to the International AIDS Vaccine Initiative. Merck & Co.'s experimental product is the most advanced in development, and the drugmaker said preliminary effectiveness data won't be available until 2008 at the earliest.

``A vaccine's going to be critical in the long run to containing the epidemic,'' said Cate Hankins, the United Nations' chief HIV scientist. ``Unless there's some striking breakthrough that we're not aware of, it's likely to be another 10 years before one is commercially available.''

Preventing the spread of the virus is essential to controlling the disease, even as effective treatment becomes more widely available. The number of people getting medicines in the hardest-hit countries rose by about 450,000 a year between 2003 and 2005, but over the same period, 10 times more people became infected every year. The cost of treating all infected people is estimated to be about $13 billion a year, assuming the lowest drug prices and no new infections.

``As far as AIDS is concerned, the quest for a vaccine is the single most important quest on the planet,'' Stephen Lewis, UN Secretary-General Kofi Annan's representative for AIDS issues in Africa said today. ``This isn't to diminish all other prevention methods but what we need is something dramatic in terms of a breakthrough. Even a modestly effective vaccine could cut the number of HIV infections by one third over a decade, saving tens of millions of lives.''

Millions Dead

More than 25 million people have died from AIDS since 1981, according to the United Nations, and groups such as the International AIDS Vaccine Initiative say a vaccine is the only way to eradicate the disease. While increased funding from organizations like the Bill & Melinda Gates Foundation has helped spur research, the failure in 2003 of VaxGen Inc.'s Aidsvax, the first widely tested vaccine, have frustrated efforts to introduce effective protection.

``It's going to be a rocky road until we have a vaccine or a cure,'' former U.S. President Bill Clinton said yesterday at the meeting. The Clinton Foundation is negotiating with generic drugmakers to drive down the price of HIV medications for developing countries.

Nowhere Near

``There's optimism, but at the same time, people have been working on this for 20 years and we're still nowhere near a vaccine,'' said Gerald Voss, head of HIV vaccine programs at London-based GlaxoSmithKline Plc.

Scientists, activists and company representatives are meeting this week at the 16th International AIDS Conference in Toronto to discuss ways to accelerate vaccine research.

The main hurdles to developing an inoculation are scientific, said Wayne Koff, chief of vaccine research at the New York-based International AIDS Vaccine Initiative, a nonprofit group that has spent more than $200 million on studies. And though funding rose to about $759 million in 2005, more than $1.2 billion a year may be needed.

Researchers at Whitehouse Station, New Jersey-based Merck have spent 10 to 15 years trying to come up with a vaccine, a challenge that has stumped scientists around the world because the virus mutates so effectively and often.

IAVI today called for new scientific and policy initiatives to speed up vaccine development. More streamlined clinical trials could cut three to five years off the time now required for vaccine development, said Seth Berkley, the group's chief executive.

Constantly Changing

No vaccine candidate has yet been capable of neutralizing all forms of the virus that are in circulation, IAVI's Koff said.

``It's quite smart at keeping itself alive,'' said Robin Isaacs, executive director of infectious-disease research at Merck. ``Because of its very effective replication system, it ends up mutating constantly and as it does, it changes the way the virus looks to the immune system. If you make an antibody against what it looks like today, tomorrow it's mutated and it doesn't look like that any longer.''

Researchers have had a hard time with the HIV virus because the usual approach to immunization -- boosting the antibodies that flush an infection away before it takes hold --doesn't work with HIV. Researchers are now looking at other ways of stimulating the immune system.

Because the virus attacks the immune system itself, it will be difficult to find a vaccine that's widely effective, the UN's Hankins said.

Not Expecting

``We're not expecting a vaccine that's going to be at the level of efficacy you'd need for complete protection,'' she said. ``But even if a vaccine had a 30 percent efficacy, it could be included among prevention tools.''

Merck is testing a product that may work to prevent HIV infection from causing disease. Merck's vaccine doesn't rely on the typical approach of teaching the body to recognize the virus and create antibodies to ward it off, Isaacs said. Instead, the vaccine is designed to improve the effectiveness of the killer T-cells that seek and destroy infected human cells.

Merck's vaccine is the most advanced in testing and the company expects to have some data in 2008 or 2009. The drugmaker will enroll a total of 3,000 patients in North and South Americas, Australia and the Caribbean for the study.

The trial is designed to evaluate both the vaccine's ability to prevent infection and whether people who do become ill develop a less harmful version of the virus, Isaacs said.

Even if the study works, it is absolutely not going to end the search for a vaccine, Isaacs said.

Sanofi, Glaxo

``The proof-of-concept trial is incredibly important because if it works, it will be the first time we've done something that works,'' he said. ``It will merely open the flood gates for wanting to do better.''

Sanofi-Aventis SA and GlaxoSmithKline are working on vaccine candidates in earlier stages of testing.

Because of the amount of time it will take to get a vaccine to market, health workers have been urging people to focus on other kinds of prevention. This includes encouraging the use of condoms and as well as more testing of other methods, such as vaginal gels, male circumcision and using drugs already prescribed for people infected with HIV/AIDS to prevent the disease.

``With HIV prevention, we may always have to use two methods or more,'' Hankins said. ``We don't see anything coming in and trumping everything else. People can't think a vaccine's going to do everything for them.''

To contact the reporter on this story: Carey Sargent in Geneva at Csargent3@bloomberg.net.

Last Updated: August 15, 2006 13:59 EDT