Subunit vaccines are a type of vaccine that use specific pieces of a virus or bacterium to stimulate an immune response. Instead of using the whole pathogen, these vaccines contain harmless subunits, such as proteins or sugars, that are essential for the pathogen's ability to cause disease. This targeted approach helps the immune system recognize and fight the actual pathogen if exposed in the future. One of the advantages of subunit vaccines is their safety profile, as they do not contain live components of the pathogen, reducing the risk of causing disease. Examples of subunit vaccines include those developed for diseases like Hepatitis B and Human Papillomavirus (HPV). These vaccines are effective in providing immunity while minimizing potential side effects.