Vaccine-induced seropositivity (VISP) is the phenomenon wherein a person who has received a vaccine against a disease would thereafter give a positive or reactive test result for having that disease when tested for it, despite not actually having the disease. This happens because many vaccines encourage the body to produce antibodies against a particular disease, and blood tests often determine whether a person has those antibodies, regardless of whether they came from the infection or just a vaccination. VISP is especially a concern in vaccine trials for HIV vaccine research because people who give a positive result in an HIV test, even if that result is because of a vaccine and not because of an infection, may face discrimination because of HIV infection. HIV Background In 1987 in America the first HIV vaccine was tested. HIV vaccines have been tested continually worldwide since then, but thus far, no one has developed any vaccine which reduces a person's risk of contracting HIV if exposed to that virus. Many HIV tests work not by checking a person's blood for HIV, but rather by determining whether the body's own antibodies against HIV are present in the blood. Most HIV vaccines are designed with the intent to promote the body's own production of antibodies which would combat HIV. Regardless of whether they are effective at stimulating the production of antibodies which fight HIV, they usually do cause the body to produce antibodies which standard HIV tests recognize as the antibodies which an HIV positive person would produce in response to HIV infection. A person who is HIV negative, and has received an HIV vaccine, and who then tests as positive in an HIV test is said to be positive because of VISP. Significance When an HIV-negative person exhibits VISP and gets an HIV-positive result from a test then that person may have difficulty donating blood or negotiating for a life insurance policy. Between 1987 and 2003 the number of persons who received experimental HIV vaccinations was about 10,000, and this number was considered small. The difficulties in determining the difference between antibodies produced by HIV infection and vaccine-induced antibodies were managed by individual vaccine research sites who had special capability to conduct additional laboratory testing on this small pool of vaccine recipients. However, at this time two new studies, the STEP Study in the US and the RV 144 study in Thailand, greatly increased