From the time that HIV was first discovered to be the virus that causes AIDS, back in
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.