A vaccine—also called a “shot” or “immunization”—is a substance that teaches your body's immune system to recognize and defend against harmful viruses or bacteria. Vaccines given before you get infected are called “preventive vaccines” or “prophylactic vaccines,” and you get them while you are healthy. This allows your body to set up defenses against those dangers ahead of time. That way, you won't get sick if you're exposed to diseases later. Preventive vaccines are widely used to prevent diseases like polio, chicken pox, measles, mumps, rubella, influenza (flu), hepatitis A and B, and human papillomavirus (HPV). No. There is currently no vaccine available that will prevent HIV infection or treat those who have it. However, scientists are working to develop one. NIH is investing in multiple approaches to prevent HIV, including a safe and effective preventive HIV vaccine. These research efforts include two late-stage, multinational vaccine clinical trials called Imbokodo and Mosaico. Other NIH-supported research aims to deliver additional HIV prevention options that are safe, effective, and desirable to diverse populations and scalable worldwide to help end the global pandemic. Learn more about how the National Institute of Allergy and Infectious Diseases, part of NIH, is approaching HIV vaccine development.