Fig. 1

Flow diagram of the study enrollment process. A total of 451 patients diagnosed with COVID-19 were admitted to Taipei Tzu Chi Hospital during the 2021 pandemic. During the pandemic, the basic data and blood samples of patients who received oxygen in the ICU and quarantine ward were collected and stored in the Biobank of Taipei Tzu Chi Hospital, Buddhist Tzu Chi Medical Foundation, and informed consent was obtained. A COVID-19 blood sample biobank was set up for storage during the 2021 pandemic. Of 451 patients, basic data of 232 patients with COVID-19 from the Biobank were retrieved and included in this retrospective cohort study, which was approved by the Institutional Review Board (IRB) of Taipei Tzu Chi Hospital, Buddhist Tzu Chi Medical Foundation. After screening the patients’ electronic medical records, 45 patients with uncomplicated-to-mild COVID-19 were excluded owing to zero risk of developing sepsis until discharge from the hospital. Blood specimens were insufficient in six patients. A total of 181 patients with COVID-19 of at least moderate severity were examined for eligibility. To determine the associations of sepsis, seven and 12 patients who had co-infection or had no blood specimens within 48 h after admission, respectively, and six patients with severe anemia were excluded. Finally, 156 patients who had not previously received vaccinations were enrolled in the study