Antibiotics cannot be used to treat an influenza virus infection. Antibiotics kill or inhibit bacteria and should only be used to treat bacterial infections. Viral infections, like influenza, require a different treatment. Still, antibiotics can be useful during the flu season. In fact, influenza virus infection causes destruction of cells of the respiratory tract, resulting in a great deal of debris that needs to be removed and replaced by new vital cells. This is a very active process that starts immediately after the initial influenza virus infection. The damaged tissue with the debris may however serve as a feeding ground for pre-existing bacteria or bacteria that infect the patient after they became infected with an influenza virus. Bacteria that are notorious for causing ‘secondary bacterial pneumonia’ are pneumococci, although several other bacteria may play a role. Obviously, complications of influenza caused by bacteria, especially when they occur in high-risk individuals such as the frail and elderly, should be treated with antibiotics.