Study Participants

The participants were recruited as part of two separate studies. Both studies were conducted in accordance with the general principles of the Declaration of Helsinki, with all participants giving written informed consent.

This study formed part of a wider study in British military personnel (MCOVID) of the effects of COVID-19 infection on their subsequent health (6). All patients apart from two had symptoms that began either in 2020 or in January 2021. For the other two patients, one had a symptom onset date in February 2021 and one in April 2021. No patient had received a vaccination for COVID-19 in advance of the onset of symptoms. The cohort also contained a number of healthy control subjects who had not had symptoms of COVID-19 infection and who had negative antibody tests. For a few individuals who contracted COVID-19 very early in the pandemic before widespread laboratory testing was available, the diagnosis was based on clinical history together with the radiological appearance of the lungs. For all other patients, the diagnosis was confirmed by laboratory testing. The participants were grouped by severity of acute infection into 1) Control: those who had no evidence of having had COVID-19; 2) Community: those who had COVID-19 and were managed in the community; 3) Ward: those who had COVID and were managed in hospital without admission to an intensive care unit (ICU); and 4) ICU: those who had COVID-19 and were admitted to an ICU for management of the disease. All but two of those admitted to ICU underwent invasive mechanical ventilation (IMV), and one also received extracorporeal membrane oxygenation (ECMO). The study was approved by the Ministry of Defence Research Ethics Committee (reference number: 1061/MODREC/20).

Participants were patients who had been hospitalized with COVID-19 pneumonia and who were recruited from a dedicated post-COVID-19 follow-up outpatient clinic in the Oxford University Hospitals NHS Foundation Trust. The date of admission to hospital with COVID-19 for the patients varied between March 2020 and February 2021. Participants were grouped by severity of acute infection into 1) Basic/O₂: patients who had COVID-19 and were managed in hospital with a maximum of simple O₂ therapy; 2) HFNC/CPAP: patients who had COVID-19 and were managed in hospital with maximum therapy of O₂ either via a high-flow nasal cannula (HFNC) or via continuous positive airway pressure (CPAP); and 3) IMV: patients who had COVID-19 and were managed with invasive mechanical ventilation (IMV). The study, C-MORE-Lung Physiology, was approved by the North West–Preston Research Ethics Committee (reference number: 20/NW/0235).