FLUAD Tetra is an influenza vaccine designed to protect against four strains of the flu virus. It is an inactivated vaccine, meaning it contains killed virus particles, which stimulate the immune system to produce antibodies without causing the disease. This quadrivalent vaccine targets two influenza A virus strains and two influenza B virus strains, providing a broader range of protection compared to trivalent vaccines. FLUAD Tetra is unique because it includes an adjuvant, an ingredient that helps to enhance the body's immune response to the vaccine, making it particularly effective in older adults. It is administered via injection, typically into the upper arm, and is recommended annually to protect against the evolving strains of the flu virus.