Severe illness and even death are likely to result if you develop another respiratory infection after catching the flu. Now, however, a team of researchers has determined that if you reverse the order of infection, pneumococcus bacteria may actually protect against a bad case of the flu. The bacterial protein pneumolysin, a bacterial virulence factor, might protect certain immune system cells (macrophages) in the alveoli of the lungs, preventing inflammation and, thus, pneumonia.

Source: Bacterial colonization prior to catching flu may protect against severe illness