Timing, case ascertainment, inclusion and exclusion criteria
We reviewed HES data for all completed episodes of hospital care in England with a discharge date from 1st March to 31st October 2020 that involved a diagnosis of COVID-19. Patients aged < 18 years were excluded. Cases of COVID-19 were identified using the International Statistical Classification of Disease and Related Health Problems 10th edition (ICD-10) codes U071 and U072.
Critical care (high dependency unit (HDU) or intensive care unit (ICU)) admissions and those receiving advanced respiratory support were identified.