Trivalent vaccines are designed to protect against three different strains of a virus or bacteria. They are commonly used for diseases like influenza, where the vaccine targets three specific strains of the influenza virus. By including multiple strains, these vaccines aim to provide broader immunity and reduce the risk of illness during outbreaks. These vaccines work by stimulating the immune system to recognize and fight off the targeted pathogens. When a person receives a trivalent vaccine, their body produces antibodies that help defend against the three included strains, enhancing overall protection and contributing to public health efforts in controlling infectious diseases.