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Why is an AIDS vaccine so difficult to create?
Last reviewed: 01.07.2025
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For decades, the search for an HIV vaccine has been like searching for the Holy Grail.
However, despite many years of research and multi-million dollar investments in research, the goal has still not been achieved.
Recent research by Oregon Health and Science University scientists has explained why a slightly weakened, safe Simian Immunodeficiency Virus (SIV), similar to the human immunodeficiency virus (HIV), could prevent rhesus macaques from becoming infected with a highly virulent strain, but treating people with the technology remained risky because the highly weakened virus had no effect at all.
The study was conducted at the Institute for Vaccine and Gene Therapy and was published in the journal Nature Medicine.
Traditionally, two methods are used to create vaccines to combat infectious diseases. In the first case, live but weakened strains are not strong enough to provoke a disease, but the immune system reacts to them, is activated, and in the future can detect a similar full-fledged virus and effectively fight it. In the second case, dead forms of the strain are used. The principle of action of these two types of vaccines is the same.
In the early 1990s, a slightly weakened form of the simian immunodeficiency virus demonstrated the ability to prevent some primates from becoming infected with the dangerous full-blown virus in the future, but in some individuals the vaccine itself caused AIDS. Attempts to weaken the virus further failed—the vaccine simply lost its effectiveness.
Therefore, the task of scientists remains to find the golden mean: to create a vaccine that is not too strong (otherwise it will lead to AIDS infection) or too weak (otherwise it will not be effective). Perhaps the study discussed in this article is a big step forward on this difficult scientific path.
A group of scientists led by Louis Picker, director of the Institute for Vaccine and Gene Therapy, discovered that protection against infection is provided by antiviral T cells, which remain in large quantities in lymphoid tissue as long as the weakened virus lives. If the virus weakens too much or dies, then the T cells become less active, and the body loses its previous protection. Therefore, unlike most other vaccines, the HIV vaccine can probably only be effective if it is constantly present in the body.
Picker’s team has refined another robust virus called cytomegalovirus (CMV) that can be used to make the body’s immune system more effective at fighting the viruses that cause AIDS. In May 2011, the scientists conducted a study that confirmed the effectiveness of the experimental vaccine. It completely controlled the immunodeficiency virus in a significant number of infected monkeys.
"This is a huge step forward. We were amazed by the results," said Wayne Koff, director of the International AIDS Vaccine Initiative. "This drug allows you to completely control the process, under its influence the immune system is able to expel the virus from the body."
Unlike the previously used experimental drug with adenoviruses AAV, which did not prevent the development of HIV infection, the modified cytomegalovirus is a permanent virus, that is, it remains in the body forever, while it causes almost no symptoms and provokes very strong cellular reactions. Louis Picker hopes that this vaccine will be able to stop the development of HIV infection in humans.