Between 39 million and 56 million people were sickened with the flu this flu season, which ran from Oct. 1, 2019, to April 4, 2020, preliminary CDC data shows.

Flu activity for the 2019-2020 season

CDC on Friday released its final Weekly Influenza Surveillance report for the 2019-2020 flu season. According to the report, four states were experiencing regional flu activity in the week ending on April 25, while 11 states were experiencing local flu activity, 27 states and Washington, D.C., were experiencing sporadic flu activity, and eight reported no flu activity.

By some indicators, the 2019-2020 flu season was worse than last flu season. For example, CDC's latest data shows the cumulative hospitalization rate for the flu during the 2019-2020 season was 69 per 100,000 people as of the week ending on April 25, compared with 63.6 per 100,000 at the same point last season.

According to CDC, this year's flu season led to at least 18 million medical visits and 410,000 hospitalizations. CDC found that the rate of outpatient visits for influenza-like illnesses for the week ending on April 25 remained below the national baseline of 2.4% at 1.8%. However, CDC said the rates of outpatient visits for influenza-like illnesses were above the national baseline in four of the United States' 10 regions during the week ending on April 25.

CDC estimated that there were at least 24,000 deaths related to the flu during the 2019-2020 season.

Worst flu season for children in a decade

This flu season was especially bad for children, according to CDC. The latest CDC report shows officials reported 170 pediatric deaths associated with the flu as of April 25, with one new pediatric death occurring in the week ending on April 25. The cumulative hospitalization rate for children ages four and under this season was 95.1 per 100,000 people as of the week ending on April 25.

Experts say the high number of pediatric deaths this flu season was due to the fact that both influenza A and B were dominant, leading to what was called a "double barrel" flu season. Experts say the influenza B strain is more likely to affect younger people, though they're not sure why. Some believe that older people may have some immunity to influenza B, as it doesn't mutate as much as other flu strains, meaning it's possible older people have caught the strain that circulated this season before (CDC Weekly U.S. Influenza Surveillance Report, 5/1; CDC "Flu View," accessed 5/4; CDC Preliminary In-Season 2019-2020 Flu Burden Estimates, accessed 5/4; Schumaker, ABC News, 2/21; Wesner Childs, Weather.com, 2/14; Edwards, NBC News, 2/20).