For the first time, an experimental vaccine has prevented infection with the AIDS virus, a watershed event in the deadly epidemic and a surprising result after recent failures led many scientists to think such a vaccine might never be possible.
Scientists and government leaders already have started mapping out how to try to improve the vaccine, which protected one in three people from getting HIV in a large study in Thailand.
That's not good enough for immediate use, researchers say. Still, the World Health Organization and the U.N. agency UNAIDS said the results 'instilled new hope' in the field, even though it likely will be years before a vaccine might be widely available.
'This is truly a great moment for world medicine,' said Lt. Gen. Eric Schoomaker, the U.S. Army Surgeon General. The Army helped sponsor the study, the world's largest of an AIDS vaccine.
It was the first time scientists tried preventing HIV the same way they treat it — with a combination approach. The study used two vaccines that work in different ways and that might be one reason the strategy worked, even though neither vaccine did when tested individually in earlier trials, scientists say.
The combo cut the risk of becoming infected with HIV by more than 31 percent in the study of more than 16,000 volunteers in Thailand, researchers announced Thursday in Bangkok.
That benefit is modest, yet 'it's the first evidence that we could have a safe and effective preventive vaccine,' said Col. Jerome Kim, an Army doctor who helped lead the study.
The outcome 'gives me cautious optimism about the possibility of improving this result' and developing a more effective AIDS vaccine, said Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, which co-sponsored the study.
Dozens of researchers, vaccine makers and deep-pocket donors will meet next week in New York 'to talk about where we go from here,' said Dr. Alan Bernstein, executive director of the Global HIV Vaccine Enterprise, an alliance of government officials, AIDS scientists, funders such as the Bill & Melinda Gates Foundation and the WHO. Researchers from the Thai trial, the Army and independent scientists will be at the meeting.
Scientists around the world cheered the first taste of victory.
'Since the 1980s, we've been hearing we're going to have an AIDS vaccine in 10 years. For the first time in my lifetime, it feels as though we're actually getting on the right track,' said Josh Ruxin, a Columbia University public health specialist who runs the Access Project, which helps health centers provide AIDS care in Rwanda.
The Thailand Ministry of Public Health conducted the study. The U.S. Army long has worked with the Thai government and others to develop and test vaccines and medicine to protect troops and the general public.
Even a marginally helpful vaccine could have a big impact. Every day, 7,500 people worldwide are newly infected with HIV; 2 million died of AIDS in 2007, UNAIDS estimates.
The study tested the two-vaccine combination in a 'prime-boost' approach, in which the first one primes the immune system to attack HIV and the second one strengthens the response.
They are ALVAC, from Sanofi Pasteur, the vaccine division of French drugmaker Sanofi-Aventis; and AIDSVAX, originally developed by VaxGen Inc. and now held by Global Solutions for Infectious Diseases, a nonprofit founded by some former VaxGen employees.
The study tested the combo in HIV-negative Thai men and women aged 18-30 at average risk of becoming infected.
Participants volunteered for the study and were told about the potential risks associated with receiving the experimental vaccine before agreeing to participate.
All were given condoms, counseling and treatment for any sexually transmitted infections and were tested every six months for HIV. Any who became infected were given free treatment with antiviral medicines. All participants continued to receive an HIV test every six months for three years after vaccinations ended.
The results: New infections occurred in 51 of the 8,197 given vaccine and in 74 of the 8,198 who received dummy shots. That worked out to a 31 percent lower risk of infection for the vaccine group. Two of the infected participants who received the placebo died.
Scientists don't know why the vaccine combo worked. It was the Army's idea to test the combination, said Dr. Donald Francis, a former government scientist who helped identify HIV as the cause of AIDS and now heads the nonprofit that holds the rights to AIDSVAX.
Scientists need to look at blood samples from study participants to understand why some became infected and others were protected.
Even AIDS advocates agreed more research was needed.
'We need to take a deep breath and look at all the available evidence from this trial' before urging that this vaccine be used now, said Julie Davids, a spokeswoman for the Community HIV/AIDS Mobilization Project, a New York-based prevention advocacy group.
Scientists want to know how long the vaccine's protection will last, whether booster shots will be needed and whether the vaccine helps prevent infection in gay men and drug users, since it was tested mostly in heterosexuals in the Thai trial.
The vaccine had no effect on HIV levels in the blood for those who did become infected.