A world first: Vaccine helps prevent HIV infection
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 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.
"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."
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.
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," said Dr. Supachai Rerks-Ngarm, the Thai Health Ministry
official who oversaw the trial. "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.
Recent Comments