Fig. 1

The flow chart of the matched cohorts for COVID-19 and for seasonal influenza. *January 31 is the date when the first UK COVID-19 case was confirmed; ^$up to 10 individuals free of exposure disease at the index date were randomly selected and individually matched to each exposed individual by birth year, sex, decile of Townsend deprivation index, and Charlson comorbidity index (0, 1, 2, or 3+); ^&individuals diagnosed with seasonal influenza between January 31 and October 31 from 2010 to 2019 based on primary care data and inpatient hospital data