It has been estimated that over 20 million people died and possibly half the world's population came down with the flu in this global epidemic, or pandemic. Influenza epidemics spread quickly through large populations because flu viruses are highly contagious. During flu's acute phase, respiratory tract secretions are rich in infectious virus and the disease is transmitted easily by sneezing and coughing. The incubation period lasts one to three days. Respiratory tract symptoms may be mild at first with a dry, unproductive cough, scratchy sore throat, and runny nose.
Ear infections are a common complication in children.
With no complications, acute symptoms usually subside after two or three days and the fever ends, although it may last as long as five days. Weakness and fatigue may persist for several weeks. Today, we have several ways to defend people from influenza. The most important tool is immunization by a killed virus vaccine. Flu vaccines are licensed by FDA, and the exact composition of the vaccine varies each year, depending on the flu strains scientists expect to be most common.