What is vaccine-induced seropositivity, or VISP?
Antibodies are made by the body to help stop infections. They are naturally made in response to infection to prevent people from being reinfected by the same microorganisms, such as viruses.
Most vaccines tell the body to make antibodies to protect against a virus without needing to be infected with the actual virus. If someone gets a human immunodeficiency virus type 1 (HIV‑1) vaccine in a research program, or clinical study, their body will likely make antibodies to HIV.
Regular HIV tests look for antibodies, not for the virus itself. These tests cannot tell if antibodies were made in response to an HIV vaccine or acquisition of the HIV virus. So, if someone gets an HIV test after getting an HIV vaccine, the test might look as if they acquired HIV, even if they have not. This is called vaccine-induced seropositivity (VISP), also known as vaccine-induced seroreactivity (VISR).
To avoid this confusion, people who have received an HIV vaccine should get a special HIV test that looks for the virus itself, which is generally known as a polymerase chain reaction (PCR) test (for other tests, please see the FAQ).
A test that indicates you have acquired HIV-1 when you have not (for example, in the case of VISP) can cause problems. It can be hard for people to prove they do not have HIV when they need to buy insurance, get a visa to travel, or join the military. It can also cause trouble with doctors, partners, employers, and others who might treat individuals they believe to be living with HIV unfairly. Additionally, it can lead to unnecessary medical treatment.
(Adapted from HIV Vaccine Trials Network. The right HIV test. Accessed July 22, 2024. https://www.hvtn.org/participate/visp-and-hiv-testing.html, and from BridgeHIV. What you need to know about vaccine-induced sero-positivity (VISP). Accessed July 22, 2024. https://bridgehiv.org/trialsandvials/visp/)