2018-19 Flu Season Separated by Two Waves Was Longest in Decade

The 2018-19 influenza (flu) season was both the longest in a decade and marked by two separate waves of influenza A, according to the Centers for Disease Control and Prevention (CDC). During the initial surge between October and mid-February, an H1N1 strain dominated, followed by an H3N2 strain beginning in mid-February that lasted through midMay. The H3N2 strain is known to cause more severe symptoms than H1N1. “It was quite an unusual season in that we almost had two seasons in one,” said Richard Webby, a flu scientist on the World Health Organization’s influenza vaccine advisory board and a member of the St. Jude Children’s Research Hospital’s Department of Infectious Diseases. According to Webby, it’s not unusual for an influenza A strain to be followed by a smaller wave of an influenza B strain; however, this longer-than-usual season had two almost similar peaks of activity from two strains of influenza A.

Despite its length and unusual pattern, CDC considers the season to be of only moderate severity both overall and for each age group. During the season in the U.S., the flu caused between 37.4 million and 42.9 million illnesses, between 531,000 and 647,000 hospitalizations and between 36,400 and 61,200 deaths. Deaths have markedly declined over the seasons, but the 2017-18 season was the deadliest in four decades with 80,000 deaths, including 180 children. By comparison, there were only 116 laboratory-confirmed deaths of children caused by the flu during the 2018-19 season.