Is there a vaccine coming? Where are we now?
The Final Declaration of
Commitment on HIV/AIDS prepared by the United Nations General Assembly in
2001 states the UN pledge to:
(89.) “Encourage increased
investment in HIV/AIDS-related research, nationally, regionally and
internationally, in particular for the development of sustainable and
affordable prevention technologies, such as vaccines and microbicides, and
encourage the proactive preparation of financial and logistic plans to
facilitate rapid access to vaccines when they become available.”
Extensive combinations of
HIV/AIDS medications (often called the “AIDS cocktail”) have already changed
the face of AIDS and helped to tremendously prolong life for many people
living with HIV and AIDS. However, there is still no cure for HIV/AIDS, and
scientists around the world agree that the best measure to take in the fight
against this global epidemic is prevention. The key to successful prevention
work, many believe, will come through the development of an HIV vaccine. Due
to the complex infections and the constantly changing nature of the virus,
however, a 100% effective HIV vaccine may still be more than a decade away.
Why is it so difficult?
First, human immune system
responses are multi-part and difficult to measure. During this process,
researchers must not only determine which immune responses to target, but
evaluate whether specific responses should be addressed one at a time, or a
combination of many responses.
Second, there are many strains
of the HIV virus. These type differences are genetically subtle, but they
require vastly different approaches in treatment. A truly effective
HIV-preventive vaccine must somehow reach a wide range of HIV strains, and
so it must find ways to work through a variety of treatment methods.
Third, perhaps the biggest
challenge facing the development of an HIV vaccine is human behavior, which
is unpredictable, very difficult to change, and impossible to account for in
a laboratory setting. When human behavior is factored in, a vaccine that
proves effective in the enclosed environment of a clinical trial may have
little or no effect or protection in the real world.
Testing on Animals
All experimental vaccines must
undergo complete testing on animals before being tested on humans. However,
HIV vaccines often act very differently within animal subjects, which points
to changes needing to be made in the experimental vaccines themselves,
making their effectiveness more predictable before the project continues to
the human testing phase.
Testing on Humans
In the process of testing on healthy (HIV-negative) human volunteers, there
are three main phases of clinical trials:
Phase I
(12-18 months): a small number
of volunteers are used to test the safety and various doses of the vaccine
Phase II
(up to 2 years): hundreds of volunteers are used to test the safety and
monitor immune responses to the vaccine
Phase III
(3-4 years): thousands of
volunteers are used to test the safety and measure effectiveness of the
vaccine
If (and only if) these three phases are successfully completed, the FDA
(Food and Drug Administration) can consider licensing the vaccine for public
distribution.
Since experimental vaccines
never contain whole or live HIV, there is no possible way that the
vaccine can cause HIV or AIDS. However, volunteering as a human test
subject for an experimental HIV vaccine will result in an HIV-positive
serology in those vaccinated. Since some of the main issues facing
HIV-positive people today are those of stigma and discrimination, there is a
fear that volunteers who may test HIV-positive under certain test conditions
(even if they are not infected) might face similar types of prejudices and
stereotypes. Volunteers are generally required to go through training prior
to becoming a human test subject, in order to help them prepare for issues
of stigma and discrimination.
HIV Vaccine Types
HIV vaccine trials have been
ongoing for many years, facing many obstacles since the virus appears to be
constantly changing form and building new defenses. A bit of science
regarding the main types of vaccines being tested:
This is a simple diagram of
the HIV virus. Experimental vaccines never use whole or live HIV.
Instead, scientists extract small parts of the virus, which are then altered
in a laboratory to create synthetic copies. Once in the body, the vaccine
should produce either antibodies or cytotoxic T cells, in order to fight
infection.
There are six main types of
experimental HIV vaccines:
1. Peptide Vaccine:
made of tiny pieces of peptides (protein) from the virus.
2. Recombinant Subunit
Protein Vaccine: made of slightly bigger pieces of proteins found on
the surface of the virus.
3.DNA Vaccine: made
of a small number of HIV genes inserted into plasmids (DNA pieces), which
produces proteins very similar to real HIV proteins.
4.Live Vector Vaccine:
non-HIV viruses genetically designed to carry genes that encode HIV
proteins. The genes are carried in to the body through a vector. This
vaccine is the most similar to the HIV virus itself, but is not harmful.
5. Virus-like Particle
Vaccine (Pseudovirion Vaccine): a non-infectious model that resembles
HIV and has one or more, but not all, of the HIV proteins.
6. Vaccine Combination
(Prime-Boost Strategy): the use of any two vaccines in succession to
create a stronger immune response.
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