Monovalent vaccines are designed to protect against a single strain of a specific pathogen, such as a virus or bacterium. By targeting only one type of infectious agent, these vaccines can provide a focused immune response, helping the body to recognize and fight off that particular pathogen effectively. An example of a monovalent vaccine is the measles vaccine, which specifically targets the measles virus. These vaccines are often used in public health programs to control outbreaks of diseases caused by specific pathogens, ensuring that individuals are immunized against the targeted infection.