World AIDS Vaccine Day was observed on 18 May 2026 to raise awareness about the need for a vaccine against HIV (Human Immunodeficiency Virus). HIV attacks the body’s immune system and can lead to AIDS (Acquired Immunodeficiency Syndrome) if left untreated. Also known as HIV Vaccine Awareness Day, the occasion honours the scientists, doctors, volunteers and health workers involved in HIV vaccine research. The observance traces back to a 1997 speech by Bill Clinton calling for an effective HIV vaccine, and the first such day was held on 18 May 1998.