A monovalent vaccine is designed to protect against a single strain of a specific pathogen, such as a virus or bacterium. This type of vaccine focuses on eliciting an immune response to one particular antigen, making it effective for targeting diseases caused by that specific strain. For example, the monovalent influenza vaccine targets only one strain of the influenza virus. Monovalent vaccines are often used in situations where a specific strain poses a significant threat, such as during an outbreak. They can be particularly useful in controlling diseases like measles or mumps, where the targeted strain is responsible for the majority of infections.