To investigate the variations in the humoral response to vaccines for the prevention of COVID-19 in liver transplant patients based on the type of immunosuppressive therapy adopted (tacrolimus based vs no-tacrolimus based) and immunosuppressive blood levels.

Inclusion Criteria:

• Liver transplanted patients >18 years of age.
• Patients who underwent liver transplantation between 01/2015 to 12/2021.
• Patients who underwent liver transplantation at "Policlinico Tor Vergata, Rome, Italy".
• Patients who have had three doses of a vaccine for the prevention of COVID-19.
• Patients who have had three doses of a SARS-CoV-2 vaccine and who have contracted SARS-CoV-2 infection.

Exclusion Criteria:

• Patients who have more or less than three dose of a vaccine for the prevention of COVID-19
• Patients not vaccinated for prevention of SARS-CoV-2 infection.
• Patients who have had three doses of a vaccine for the prevention of COVID-19 prior to liver transplantation.

Liver transplant recipients who underwent SARS-CoV-2 vaccination (3 doses)