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PREVENTION AND CURE
SAFER SEX -
Globally, the most common
route of HIV transmission is through unprotected
anal or vaginal intercourse. The risk can be
eliminated by avoiding intercourse, or minimized
by using a condom or "female condom", since HIV
cannot pass through an intact latex barrier.
HIV transmission through oral sex is possible
but rare, and AIDS organizations in most
countries do not routinely recommend condom use
for this activity.
Many safer sex campaigns have been conducted to
encourage the general public and the groups most
at risk from HIV to avoid unprotected sex.
However, research on health promotion repeatedly
shows that the simple provision of information
is usually not in itself sufficient to lead to
behaviour changes. That may require additional
factors; for example, campaigns are more likely
to succeed if they present acceptable and
achievable options, and are reinforced by peer
pressure in favour of certain forms of behaviour
and against others.
The most successful safer sex campaigns were
those conducted by and for urban gay communities
in the 1980s, where the reduction in unprotected
anal intercourse has been identified as the
greatest health-related behaviour change ever
achieved.
VACCINES -
Efforts are under way to
develop an effective vaccine for HIV that could
be either protective (preventing infection if an
immunized person is exposed) or therapeutic
(slowing immune destruction or prolonging
survival in people who are already infected).
Most of the current experimental vaccines
consist of one or more of HIV's structural
proteins, such as the core protein p24 or the
outer “envelope” proteins gp120 and gp160, used
in combination with an adjuvant to boost the
immune response.
Trials to date have been largely discouraging.
Studies of several different therapeutic
vaccines have found that some are immunogenic
(they stimulate immune responses) but all have
failed to show any effects on disease
progression or survival rates. Ongoing studies
are exploring whether the use of therapeutic
vaccines combined with HAART may be more
effective than current treatment strategies that
use HAART alone.
Researchers working on preventive vaccines face
a range of technical problems, including the
difficulty of producing a vaccine that might
offer protection against the range of HIV
sub-types (or clades) found around the world,
and HIV's ability to mutate rapidly so that its
surface proteins are no longer recognized by the
body's immune response. An effective vaccine
would need to protect the individual against
infection when exposed to either free HIV
particles or HIV-infected cells, and to
stimulate effective immune responses when the
virus enters the body through the blood (such as
during injecting drug use or occupational
exposure) or across mucous membranes (such as
during sexual intercourse).
The first large-scale efficacy trial of a
protective HIV vaccine, AIDSVAX from VaxGen,
ended in disappointment in 2003 when it was
shown not to have slowed the progress of the
disease. Scientists had earlier disagreed
strongly over whether AIDSVAX, which was
comprised of genetically engineered versions of
the gp120 protein found on the surface of HIV,
was likely to be effective. Several other
large-scale preliminary studies of protective
vaccine candidates are under way in high-risk
populations such as gay and bisexual men, and in
areas of the world with high incidence of HIV
infection, such as Thailand, Brazil, and India.
Some studies are evaluating a strategy known as
"prime-boost", in which an initial immunization
with one type of HIV vaccine is followed by a
different type of vaccine, to try to stimulate
different parts of the immune system. Although
there have been promising results from animal
tests of this approach, it will be many years
before results of human studies are available.
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