The study is to evaluate the safety and efficacy of COVID-19 convalescent plasma (CCP) transfusion to prevent COVID-19 in adult recipients following hematopoietic stem cell transplantation.

72 patients will be randomized in a 1:1 ratio to receive either CCR (36 patients) or not (36 patients). Patients in the CCP group will receive 200 ml of CCP at +14 days, +28 days, +2 months, and +3 months following hematopoietic stem cell transplantation. Patients in the control group would be routinely given oral ursodeoxycholic acid for +14 days after transplantation.

The primary goal of the study is to evaluate the safety of CCP and the incidence of COVID-19 infection within +28 days after the last infusion of CCP.

Inclusion Criteria:

1. receive hematopoietic stem cell transplantation
2. Be ≥ 16 years of age on the day of enrollment.
3. Understand the study procedures, alternative treatment available, and risks involved with the study, and voluntarily agree to participate by giving written informed consent.

Exclusion Criteria:

1. Positive serological response to known HIV or active hepatitis C virus.
2. Patients with mental illness or other conditions that do not meet the requirements of research treatment and monitoring.
3. Unable or unwilling to sign consent form.
4. Patients with other special conditions assessed as unqualified by the researchers.
5. Patients suffered COVID-19 infection between day 0 and infusion of CCP after transplantation.

Drop-out and Withdrawal Criteria

1. Failure of engraftment within 30 days of transplantation;
2. Patients who are not compliant with the requirements of the study and fail to follow the study plan.
3. Patients receiving prophylaxis for COVID-19 infection by methods other than this protocol during the trial.
4. A patient may withdraw from the study if he/she does not wish to continue participating in the study, and the date and reason for withdrawal shall be recorded. The investigator may also decide to discontinue a patient from the clinical study if there is an unacceptable risk.