The term "quadrivalent" refers to something that has four valences or is capable of forming four bonds. In chemistry, this often describes an atom, such as carbon, which can bond with four other atoms to create various compounds. Quadrivalent elements play a crucial role in the formation of complex molecules. In the context of vaccines, a quadrivalent vaccine is designed to protect against four different strains of a virus. For example, the quadrivalent influenza vaccine targets four strains of the influenza virus, providing broader immunity compared to vaccines that cover fewer strains. This approach helps enhance public health by reducing the spread of infectious diseases.