The 2018-2019 flu season was the longest in 10 years, according to The Centers for Disease Control and Prevention. This year's flu season lasted 21 weeks, it’s usually around 16 weeks. The reason for the long season of sickness was two waves of influenza this year. Dr. Lynnette Brammer, Epidemiologist. CDC's Influenza Division says, "the first was an influenza A -HIN1 wave and the second was an H3N2 wave and then in addition to that we saw very little influenza B activity."
Most flu seasons start off with lots of infections from influenza A viruses, which can be more severe and less responsive to vaccination than other sub types, while generally less-severe influenza B viruses often strike later.
Despite its length and unusual pattern, the CDC considers the season to be of only "moderate" severity. Influenza caused between 37.4 million and 42.9 million illnesses in the US during the 2018-19 season; between 531,000 and 647,000 hospitalizations; and between 36,400 and 61,200 deaths, the CDC estimated.