An important phenomenon of this flu is the high mortality rate of young people. In this regard, there are two hypotheses: first, the elderly have experienced the flu, so they have antibodies, so they are more resistant to the flu. Second, the immune system of young adults is good, and in the process of eliminating foreign viruses, the fever and inflammation caused are also serious; The overreaction of immune system may lead to cytokine storm, which may cause damage to human tissues or organs. If it occurs in the lungs, it may lead to the patient's breathing difficulties and death.

The Spanish flu completely disappeared within 18 months, and its strain was never really determined.