Vaccination Efficacy Against Delta Variant

All patients were treated by the medical team of the First Affiliated Hospital of Xi’an Jiaotong University between 20 December 2021, and 20 January 2022. The eligible discharged patients were screened in this retrospective study (Figure 1), and patients younger than 5 years old were excluded. Patients with incomplete and inaccurate baseline data were also excluded from this study. All patients were confirmed to infect with SARS-CoV-2 delta variant by Xi’an CDC (Center for Disease Control and Prevention). There were 31 patients who did not receive any vaccination (non-vaccination group, NV), 21 patients who received only one-dose vaccination (one-vaccination group, OV) and 60 patients who received two- or three-dose vaccination (two-vaccination group, TV). All vaccinated patients received inactivated vaccines (inactivated SARS-CoV-2 vaccine CoronaVac, and aluminium hydroxide as adjuvant. Sinovac life sciences Co. Ltd.). All patients underwent nasopharyngeal swab sample collection according to the national guidelines [16 (link)] and were diagnosed via SARS-CoV-2 nucleic acid amplification tests, and the results were confirmed by the Xi’an Center for Disease Control and Prevention. This study was approved by the Ethics Committee of the First Affiliated Hospital of Xi’an Jiaotong University, and all patients provided written informed consent. All research methods were carried out in compliance with the relevant declarations of medical ethics and the Declaration of Helsinki.