A bivalent vaccine is designed to protect against two different strains of a virus or two different viruses altogether. This type of vaccine helps the immune system recognize and fight off infections more effectively by targeting multiple threats at once. For example, the bivalent COVID-19 vaccine targets both the original strain of the SARS-CoV-2 virus and its variants, enhancing immunity. By using a bivalent approach, public health efforts can potentially reduce the spread of diseases and improve overall vaccination coverage.