HIV Vaccine: How Close Are We?

Some of the most important medical breakthroughs of the past century involved the development of vaccines to protect against viruses such as:

But one virus still thwarts those who want to create a vaccine to guard against it: HIV.

HIV was first identified in 1984. The U.S. Department of Health and Human Services announced at the time that they hoped to have a vaccine ready within two years. Despite many trials of possible vaccines, though, a truly effective vaccine is still not available. Why is it so difficult to conquer this disease? And where are we in the process?

Obstacles to an HIV vaccine

It’s so hard to develop a vaccine for HIV because it’s different from other types of viruses. HIV doesn’t fit typical vaccine approaches in several ways:

1. The immune systems of almost all people are “blind” to HIV. The immune system, which fights disease, doesn’t respond to the HIV virus. It produces HIV antibodies, but they only slow the disease — they don’t stop it.

2. Vaccines are typically made to mimic the immune reaction of recovered people. However, almost no people have recovered from an HIV infection. As a result, there’s no immune reaction that vaccines can mimic.

3. Vaccines protect against disease, not infection. HIV is an infection until it progresses to stage 3, or AIDS. With most infections, vaccines buy the body more time to clear the infection on its own before disease occurs. However, HIV has a long dormant period before it progresses to AIDS. During this period, the virus hides itself in the DNA of the person with the virus. The body can’t find and destroy all of the hidden copies of the virus to cure itself. So, a vaccine to buy more time won’t work with HIV.

4. Killed or weakened HIV viruses can’t be used in a vaccine. Most vaccines are made with killed or weakened viruses. Killed HIV doesn’t work well to produce an immune response in the body, though, and any live form of the virus is too dangerous to use.

5. Vaccines are typically effective against diseases that are rarely encountered. These include diphtheria and hepatitis B. But people with known risk factors for HIV might be exposed to HIV daily. This means there’s more chance for infection that a vaccine can’t prevent.

6. Most vaccines protect against viruses that enter the body through the respiratory or gastrointestinal systems. More viruses enter the body in these two ways, so we have more experience addressing them. But HIV enters the body most often through genital surfaces or the blood. We have less experience protecting against viruses that enter the body in those ways.

7. Most vaccines are tested thoroughly on animal models. This helps ensure that they’re likely to be safe and effective before they’re tried on humans. However, no good animal model for HIV is available. Any testing that has been done on animals has not shown how humans would react to the tested vaccine.

8. The HIV virus mutates quickly. A vaccine targets a virus in a particular form. If the virus changes, the vaccine may not work on it anymore. HIV mutates quickly, so it’s hard to create a vaccine to work against it.

Prophylactic vs. therapeutic vaccines

Despite these obstacles, researchers continue to try to find a vaccine. There are two main types of vaccines: prophylactic and therapeutic. Researchers are pursuing both for HIV.

Most vaccines are prophylactic, which means they prevent a person from getting a disease. Therapeutic vaccines, on the other hand, are used to increase the body’s immune response to fight disease that the person already has. Therapeutic vaccines are also considered treatments.

Therapeutic vaccines are being investigated for several conditions such as:

An HIV vaccine would theoretically have two goals. First, it could be given to healthy people to protect them from HIV infection. This would make it a prophylactic vaccine. But HIV is also a good candidate for a therapeutic vaccine. Researchers hope that a therapeutic HIV vaccine could reduce a person’s viral load.

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