Influenza is rare? Maybe rare for you if you habitually get the flu shot twice a year, but even then the efficacy of the flu shot can be as low as 50%. Influenza is very common, most people have experienced it.
Adults catch real flu about once every five years, scientists calculate, based on a field study in China.
https://www.bbc.com/news/health-31698038
on average, about 8% of the U.S. population gets sick from flu each season, with a range of between 3% and 11%, depending on the season.