WASHINGTON (Reuters) - The use of a weakened strain of live HIV
-- the virus that causes AIDS -- in mass vaccination campaigns
may actually increase death rates from the disease in many
countries, researchers said on Monday, describing a medical
A research team headed by a University of California at Los
Angeles scientist created a sophisticated mathematical model to
predict for the first time the outcome of future vaccination
efforts using an AIDS vaccine made from an attenuated -- or
weakened -- form of live HIV.
To their surprise, the researchers said such a vaccine would
increase death rates in countries where the AIDS epidemic was
either low or moderate, while the same vaccine would reduce
greatly the death rates in nations where AIDS was rampant.
"The exact same vaccines could be beneficial in one country,
but detrimental in another," Dr. Sally Blower, professor of
biomathematics and a member of the UCLA AIDS Institute, said in
a telephone interview.
Blower said an attenuated vaccine might prove worthwhile only
in developing countries facing perilous transmission rates,
such as those in sub-Saharan Africa. "If you use such a
vaccine, for example, in the United States, you would
definitely make things much, much worse," she said.
Such a vaccine could be instrumental in fighting the disease
because it generates a strong immunity, but it could also cause
AIDS in some vaccinated people because of its use of the live
Blower, the study's principal investigator, described a
"Catch-22" situation for public health officials around the
world if researchers fashioned an AIDS vaccine using a live
"The vaccines have the potential to do a great deal of good,
but they also have the potential to do harm. That's the essence
of the Catch-22 problem," Blower said.
"You can develop very effective vaccines. But they may well be
the ones that are the least safe. There may be a trade-off that
people will have to consider between efficacy and safety once
these vaccines have been developed."
The development of any such vaccine is still years away. Live
attenuated vaccines have been used in the past to control such
diseases as polio, smallpox and measles.
Zimbabwe And Thailand Studied
The researchers matched their mathematical model to the current
AIDS death rates in Zimbabwe -- where one in four people in the
population of 11.3 million is infected with HIV -- and
Thailand, where 2 percent of the population of 61 million
people is infected.
The study, published in the Proceedings of the National Academy
of Sciences, found that a live-virus vaccine would wipe out the
naturally occurring strains of HIV in both countries within 50
But researchers said that in Thailand, such a vaccine would
increase the death rate if the vaccine caused more than 5
percent of the population to develop AIDS over 25 years. In
Zimbabwe, researchers said their model predicted that more
people would die of AIDS with no vaccination campaign than with
a public vaccination effort using the live HIV vaccine.
Public health officials face a difficult ethical dilemma.
"Should you kill some people for the greater good of the rest
of the people? That is a huge, huge ethical debate," Blower
said. She added that if those vaccines were developed, public
health officials would know that some people who were not
infected would develop AIDS and die because of the vaccine. But
she added that not using such a vaccine could mean "letting the
entire continent of Africa be totally destroyed."
Blower said she and her colleagues were not advocating that an
attenuated vaccine be used, but merely wanted to provide a
theoretical framework for predicting the outcome of using 1,000
different potential versions of such a vaccine.
"Vaccines are essentially the only hope of really controlling
and eradicating HIV," she said. "So we'll have to see what
people come up with in terms of effective vaccines."