This study uses data from the National Institutes of Infectious Diseases Japan to compare weekly influenza activity in the 2019/2020 vs the 2014-2019 seasons given mitigation strategies taken in 2020 to limit the spread of COVID-19.

The authors used data from 2014 to 2020 from the National Institute of Infectious Diseases Japan and grouped weekly reports into seasons (week 40 of the year through week 11 of the following year [September 30, 2019, through March 15, 2020, for the 2019/2020 season]. They assessed the weekly influenza activity in each season  and estimated the change in influenza activity after the SARS-CoV-2 outbreak using a difference-in-difference regression model.

The data suggest that seasonal influenza activity was lower in 2020 than in previous years in Japan. The authors believe this is related to temperature, virulence, and measures taken to constrain the SARS-CoV-2 outbreak. Their findings suggest that concerns regarding the SARS-CoV-2 outbreak may have changed detection of influenza through changes in symptomatic individuals seeking medical attention or in physicians’ inclination to test for influenza.