The trivalent influenza vaccine is designed to protect against three strains of the influenza virus. Typically, it includes two strains of the influenza A virus and one strain of the influenza B virus. This vaccine helps the immune system recognize and fight off these viruses, reducing the risk of illness during the flu season. Administered through an injection, the trivalent vaccine is recommended for most individuals aged six months and older. It is especially important for high-risk groups, such as the elderly, young children, and those with certain health conditions, to receive the vaccine to prevent severe complications from the flu.