The summer isn’t a ripe time for most influenza strains because, researchers posit, the cold and dry weather conditions of the fall and winter make it easier for flu viruses to thrive (dryness and low humidity may actually also make it easier for the flu to attack the lungs). That’s not to say it never happens—but usually, people who present flu-like symptoms in the late summer or beginning of September (such as fever, body aches, a cough, congestion, diarrhea, etc.) actually have some other kind of virus such as the one that causes gastroenteritis (which is commonly, and misleadingly, referred to as the stomach flu).
So how long is the flu season?
The more commonly accepted timeline of the flu season, when people are usually hospitalized for flu and flu-like illnesses, lasts between October and late April/early May. Peak flu season most commonly occurs between December and February, with February typically presenting the highest number of cases, according to CDC data. That trend will likely hold true for the 2018 season, too.