The primary purpose of vaccines in medicine is to stimulate an immune response, providing protection against infectious diseases. Vaccines contain weakened or inactivated parts of a specific pathogen, such as viruses or bacteria, which train the immune system to recognize and combat the actual pathogen if encountered later. This proactive approach reduces the risk of disease outbreaks, minimizes the severity of infections, and contributes to herd immunity, which helps protect vulnerable populations. Vaccination plays a crucial role in public health and disease prevention efforts worldwide.