Influenza A, B, and C viruses are widespread globally and infect a significant number of children and adults each year.
For example, during the 2017–2018 flu season, there were 30,453 cases of hospitalization due to influenza, according to the Centers for Disease Control and Prevention (CDC).
During the same period, 185 children died as a result of the flu, approximately 80 percent of whom had not received a flu shot that season.
Estimates place the effectiveness of current flu vaccines at 40 percent, which means that the shot cuts the risk of someone seeking influenza-related medical help by two-fifths.
Current flu shots are not effective against all influenza strains, so people need to have another vaccine each year. However, new research may soon change this, as scientists have found that a particular type of immune cell can protect against all influenza types.