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.
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 Bangkok.
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 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,
which 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 statement.
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 generation."
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.
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 AIDS.
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.
Associated Press Medical Writer Marilynn Marchione reported
from Minneapolis.
On the Net:
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SOURCE: The Associated Press