 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 antiviral 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 into 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 two HIV vaccines tested in Thailand That prevented 31 percent 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 called visp vaccine induced seropositivity Other tests can be done to tell the difference between 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 This video has been produced by Eureka Science in collaboration with Bridge HIV Just in touch with Eureka Science, like us on Facebook, follow us on Twitter, or subscribe to our YouTube channel Or visit us at EurekaScience.org Thank you for watching