BANGKOK (AP) - 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. Recent failures led many
scientists to think such a vaccine might never be possible.
The World Health Organization and the U.N. agency UNAIDS said
the results "instilled new hope" in the field of HIV vaccine
research, although researchers say it likely is many years before a
vaccine might be available.
The vaccine - a combination of two previously unsuccessful
vaccines - cut the risk of becoming infected with HIV by more than
31 percent in the world's largest AIDS vaccine trial of more than
16,000 volunteers in Thailand, researchers announced Thursday in
Even though the benefit is modest, "it's the first evidence
that we could have a safe and effective preventive vaccine," Col.
Jerome Kim told The Associated Press. He helped lead the study for
the U.S. Army, which sponsored it with the National Institute of
Allergy and Infectious Diseases.
The institute's director, Dr. Anthony Fauci, warned that this is
"not the end of the road," but he said he was surprised and very
pleased by the outcome.
"It gives me cautious optimism about the possibility of
improving this result" and developing a more effective AIDS
vaccine, Fauci said. "This is something that we can do."
The Thailand Ministry of Public Health conducted the study. The
U.S. Army has long worked with that government and others to
develop and test vaccines and medicines to protect troops and the
The study used strains of HIV common in Thailand. Whether such a
vaccine would work against other strains in the U.S., Africa or
elsewhere in the world is unknown, scientists stressed.
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.
"Today marks a historic milestone," said Mitchell Warren,
executive director of the AIDS Vaccine Advocacy Coalition, an
international group that has worked toward developing a vaccine.
Warren was not involved in the study.
"It will take time and resources to fully analyze and
understand the data, but there is little doubt that this finding
will energize and redirect the AIDS vaccine field," he said in a
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.
ALVAC uses canarypox, a bird virus altered so it can't cause
human disease, to ferry synthetic versions of three HIV genes into
the body. AIDSVAX contains a genetically engineered version of a
protein on HIV's surface. The vaccines are not made from whole
virus - dead or alive - and cannot cause HIV.
Neither vaccine in the study prevented HIV infection when tested
individually in earlier trials, and dozens of scientists had called
the new one futile when it began in 2003.
"I really didn't have high hopes at all that we would see a
positive result," Fauci confessed.
The results proved the skeptics wrong.
"The combination is stronger than each of the individual
members," said the Army's Kim, a physician who manages the Army's
HIV vaccine program.
The study tested the combo in HIV-negative Thai men and women
aged 18 to 30 at average risk of becoming infected. Half received
four "priming" doses of ALVAC and two "boost" doses of AIDSVAX
over six months. The others received dummy shots. No one knew who
got what until the study ended.
Thanad Yomha, a 33-year-old electrician from southeastern
Thailand, said he didn't expect anything in return for volunteering
for the project.
"I did this for others," Thanad said. "It's for the next
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
The vaccine had no effect on levels of HIV in the blood for
those who did become infected. That had been another goal of the
study - seeing whether the vaccine could limit damage to the immune
system and help keep infected people from developing full-blown
That result is "one of the most important and intriguing
findings of this trial," Fauci said. It suggests that the signs
scientists have been using to gauge whether a vaccine was actually
giving protection may not be valid.
"It is conceivable that we haven't even identified yet" what
really shows immunity, which is both "important and humbling"
after decades of vaccine research, Fauci said.
Details of the $105 million study will be given at a vaccine
conference in Paris in October.
This is the third big vaccine trial since 1983, when HIV was
identified as the cause of AIDS. In 2007, Merck & Co. stopped a
study of its experimental vaccine after seeing it did not prevent
HIV infection. Later analysis suggested the vaccine might even
raise the risk of infection in certain men. The vaccine itself did
not cause infection.
In 2003, AIDSVAX flunked two large trials - the first late-stage
tests of any AIDS vaccine at the time.
It is unclear whether vaccine makers will seek to license the
two-vaccine combo in Thailand. Before the trial began, the U.S.
Food and Drug Administration said other studies would be needed
before the vaccine could be considered for U.S. licensing.
"This is a world first which proves that vaccine development is
possible," Supachai said. "But this is not to the level where we
can license or manufacture the vaccine yet."
Mass-producing the vaccine, plus how to proceed with future
studies, will be discussed among the governments, study sponsors
and companies involved in the trial, Kim said. Scientists want to
know how long protection will last, whether booster shots will be
needed, and whether the vaccine helps prevent infection in gay men
and injection drug users, since it was tested mostly in
heterosexuals in the Thai trial.
The study was done in Thailand because U.S. Army scientists did
pivotal research in that country when the AIDS epidemic emerged
there, isolating virus strains and providing genetic information on
them to vaccine makers. The Thai government also strongly supported
the idea of doing the study.
(Copyright 2009 by The Associated Press. All Rights Reserved.)