1983, scientists have been working on developing a vaccine. Here we are, more than 30 years

later – so why don’t we have a vaccine yet? Oh, and by the way, what is a vaccine

and how does it work to prevent an infectious disease?

Unlike anti-viral medicines used to treat infections, vaccines work by training a person’s

immune system before exposure to a virus, so that the immune system can fight off the

virus and prevent that person from becoming infected.

HIV presents some unique challenges to developing a vaccine. First, HIV attacks the very immune

cells that are sent by the body to kill it off, and inserts its genes inside these cells.

After that happens, the only way to get rid of HIV is to kill off the infected cells.

That leads to the second challenge, which is that HIV infected cells can hide out and

remain “dormant” or asleep, making it difficult or impossible for other killer immune

cells to find it. Thirdly, every time HIV reproduces, it makes a lot of genetic mistakes.

And unlike many living things (including humans) that have certain systems in place to correct

these mistakes, HIV is a “sloppy” virus that doesn’t fix itself. So, HIV changes

over time, and it has been difficult to find a vaccine that will protect against all of

these changes.

So, how do we propose to build a vaccine? First, you should know that there is never

any live or killed HIV in a vaccine, which is a strategy used by some other vaccines

against less dangerous viruses. Also, no one participating in a vaccine study is ever exposed

to HIV as part of the study!

Now that we have that out of the way, the goal of an ideal HIV vaccine is to activate

both antibodies and T cells, so that the immune system is ready to fight off HIV. Antibodies

are proteins that attach to HIV before HIV can infect a cell, thereby preventing infection.

An example of how this works is the polio vaccine. After you get a polio vaccine, you

develop antibodies against polio that are ready to attack if you ever come in contact

with the polio virus. We’d like to develop an HIV vaccine that develops antibodies that

would attack the many strains of HIV that exist. Another strategy is to train T cells

to recognize and fight off HIV so that, when HIV enters, the T cells could kill the virus.

All HIV vaccines are made with synthetic, manufactured imitations of parts of HIV, a

strategy that can never cause infection, but can train the immune system to fight off HIV.

The most successful HIV vaccine strategy so far is a combination of 2 HIV vaccines tested

in Thailand that prevented 31% of new infections. This vaccine isn’t licensed, but scientists

are using information from this study to make more powerful and long-lasting vaccines that

can be used for populations around the world.

One thing to know is that the most common way to diagnose actual HIV infection is to

test for HIV antibodies. A person who becomes HIV infected generates antibodies against

HIV, but because they are only developed weeks after infection, they can’t prevent infection.

These antibodies can keep HIV in check for a while, but eventually HIV comes out of hiding

and causes AIDS, unless a person is treated with antiretrovirals (HIV medicines). Measuring

HIV antibodies is a relatively cheap and easy way to test whether someone has been HIV infected,

but the test doesn’t usually turn positive until several weeks or several months after

infection, because that’s the length of time it takes to develop antibodies without

a vaccine. Some people who get a vaccine will also be antibody positive, because they have

“vaccine-induced” antibodies, also known as VISP. Other tests can be done to tell the

difference between “vaccine-induced seropositivity (VISP) and actual infection. These other tests

are available at all research sites that conduct HIV vaccine trials and HIV vaccine trial volunteers

can continue to get HIV testing for free at these sites, even after the study has ended.

Over 35 million people worldwide are currently living with HIV/AIDS. Fortunately, we’re

part of the way toward developing a safe and highly effective HIV vaccine. And with a committed

and diverse partnership of community members, scientists, educators and policymakers, we

could ultimately defeat our century’s biggest epidemic.