A monovalent influenza vaccine is designed to protect against a single strain of the influenza virus. This type of vaccine is often used during outbreaks when a specific strain is prevalent, allowing for targeted immunity. It contains antigens from only one influenza virus strain, making it effective for that particular variant. These vaccines are typically updated annually to match circulating strains, as influenza viruses can change frequently. Health organizations, such as the World Health Organization, monitor these changes to recommend the most effective strains for inclusion in the vaccine. Monovalent vaccines are crucial for controlling specific influenza outbreaks.