Profile
Photos
Comments
Milestone in AIDS fight: Experimental vaccine cuts risk of HIV
infection
Thursday, September 24th 2009, 4:00 AM
BANGKOK - 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 vaccine 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 said in a
telephone interview. 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 in a telephone
interview. "This is something that we can do."
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,
the U.N. agency UNAIDS estimates.
"Today marks an historic milestone," said Mitchell Warren,
executive director of the AIDS
Vaccine Advocacy Coalition, an international group that has worked toward
develping a vaccine.
"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 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.
The study actually tested a two-vaccine combo in a "prime-boost" approach,
where 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.
The study tested the combo in HIV-negative Thai men and women ages 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.
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.
Participants were followed for three years after vaccination ended.
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.
The vaccine had no effect on levels of HIV in the blood of 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.
Also unclear is whether Thai volunteers who received dummy shots will now be
offered the vaccine. Researchers had said they would do so if the vaccine showed
clear benefit - defined as reducing the risk of infection by at least 50
percent.
Those issues, 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 will protection 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.