Vaccination is a medical process that helps protect individuals from infectious diseases. It involves introducing a small, harmless part of a virus or bacteria, called an antigen, into the body. This stimulates the immune system to recognize and fight the actual disease if exposed in the future. Vaccines can prevent serious illnesses like measles, polio, and influenza. Vaccines are usually given through injections, but some can be taken orally or as nasal sprays. They are an essential part of public health, helping to reduce the spread of diseases and protect vulnerable populations, such as infants and the elderly.