A subunit vaccine is a type of vaccine that contains only specific pieces of a pathogen, such as proteins or sugars, rather than the whole germ. This approach helps the immune system recognize and fight the actual pathogen without exposing the body to the disease itself. Subunit vaccines are often safer and can be used for various diseases. These vaccines stimulate an immune response by presenting these harmless pieces to the immune system, allowing it to learn how to combat the real pathogen in the future. Examples of subunit vaccines include those developed for diseases like Hepatitis B and Human Papillomavirus (HPV).