The failed tests represent a major setback in the global effort to
stem infections with the virus that causes AIDS. Merck had
expressed great optimism for the vaccine, which it has been
testing for a decade.
The independent Data Safety Monitoring Board, after reviewing
interim results of the study of the vaccine, recommended
discontinuing vaccinations of volunteers as the trial was headed
for failure, Merck said.
"No one really knows when and if we will ever have an effective
HIV vaccine because the virus is such a great challenge," Mark
Feinberg, vice president of medical affairs at Merck's vaccine
unit, said in an interview.
The vaccine consisted of a common cold virus loaded with three
proteins found in the HIV virus.
"The concept was that if someone getting the vaccine is later
exposed to HIV, the immune system would recognize those HIV
proteins and go after the virus," said Keith Gottesdiener, another
senior Merck research executive.
Asked if Merck would attempt to develop other HIV vaccines in the
wake of the failed trial, Gottesdiener said, "At this point, we
can't give an answer; we're just starting to look at this data and
all its implications."
The New Jersey-based company, which was developing the product in
partnership with the federally funded HIV Vaccine Trials Network,
said two other early-stage trials of the vaccine had also been
discontinued.
Study investigators have been instructed to discontinue
vaccinating volunteers and to monitor them, Merck said.
The study was aiming to determine whether the vaccine prevented
HIV infection and whether it reduced the amount of virus in those
who developed infection.
Although a number of medicines have been introduced in recent
years that control the virus and keep symptoms of the otherwise
fatal disease at bay, doctors have said a preventive vaccine is by
far the best way to control continued spread of the disease.
Millions of people have succumbed to the disease since it started
becoming prevalent in the early 1980s, with the worst outbreaks in
Africa. The virus is now believed to be spreading quickly in
India, China and other parts of Asia, fueled by unprotected sexual
contact, prostitution and shared needles among drug users.
As many as 1 million Americans are believed infected with the
virus. Many have insurance that covers the costly drug cocktails
needed to prevent uncontrolled growth of the virus. But the drugs,
which can cause serious side effects, must be taken for life
because they cannot totally eradicate the quickly mutating virus.
Merck's discontinued international trial, called STEP, involved
3,000 HIV-negative volunteers from diverse backgrounds, between
the ages of 18 and 45, at high risk of HIV infection.
An interim efficacy analysis, conducted in about 1,500 volunteers
expected to have the best response to the vaccine, showed the drug
was ineffective.
Although the vaccine has been a major hope among the medical
community, it was not deemed to have major commercial potential,
and Merck shares were little affected by the news. The shares were
up 31 cents to $51.69 in afternoon trading on the New York Stock
Exchange.
Additional reporting by Bill Berkrot