## 1 Introduction  
SARS-CoV-2 is a betacoronavirus, an enveloped virus containing a large nucleoprotein (N)-encapsulated positive sense RNA genome. The viral lipid envelope incorporates three transmembrane proteins: the spike protein (S), membrane protein (M), and envelope protein (E). Streamers of SARS-CoV-2 bind to the receptor, ACE2, on the surface of the target cells and mediate subsequent viral uptake and fusion [1].  
Some specific drugs have been approved for the treatment and prevention of SARS-CoV-2 infection:  
* Antivals: Nirmatrelvir/Ritonavir, Remdesivir, Molnupiravir;
* Monoclonal antibodies: Bamlanivimab/Etesevimab, Casirivimab/Imdevimab, Sotrovimab, Tixagevimab/Cilgavimab;
* Vaccines: mRNA vaccines, BNT162b2 (Pfizer-BioNTech) or mRNA-1273 (Moderna) and viral vector vaccine Ad26.COV2.S (Johnson & Johnson/Janssen) [2], ChAdOx1-S (Astrazeneca).  
According to the guidelines, COVID-19 vaccination is recommended, as soon as possible, for everyone who is eligible according to the CDC's Advisory Committee on Immunization Practices Vaccination [2].  
Since the beginning of the vaccination campaign, particular attention has been paid to frail patients because they are more prone to developing a serious and unfortunate clinical status. Patients with specific immunological conditions due to autoimmune diseases or those receiving immunosuppressive drugs or anti-cancer therapies have been considered as the priorities for immunization, particularly in Western countries, where, to date, they are almost fully vaccinated.  
Even if there are no available data about these populations, because they had not been enrolled in the vaccine approval trials, vaccines in patients with cancer, hematopoietic stem cell transplantation, solid organ transplantation, multiple sclerosis (MS), inflammatory bowel disease (IBD), and rheumatoid and dermatologic autoimmune disorders were administered first [3].  
Patients with organ transplantation are chronically treated with immunosuppressive that prevent the rejection of the transplanted organ but reduce immunocompetent, exposing the patient to severe forms of infections.  
[PERSON] et al. [4] documented a reduced immune response after two doses of COVID-19 vaccine in transplanted patients.  
Moreover, [PERSON] et al. [5], when evaluating the effectiveness of the second dose of Comirnaty in 40 kidney transplant patients vs. the healthy controls, failed to report a comparable IgG titers, suggesting that immunosuppression resulted in impaired protective immunity after mRNA vaccination  
Similarly, in a real-world study, [PERSON] et al. [6] reported that none of the vaccinated lung transplant patients developed anti-SARS-CoV-2 IgG, suggesting that immunosuppressivement therapy inhibits the humoral response to the COVID-19 vaccine. Furthermore, real-world data concerning vaccinated dialysis patients suggest that in these patients, the post-vaccination humoral response may be delayed and/or reduced by several factors related to the uremic condition [7].  
However, there are no definitive data regarding the efficacy of vaccine in these patients. Moreover, the lack of pre-marketing evidence in these patients signals the need for the real-world study of a vaccine benefit-risk profile in immunocompromised patients.  
Therefore, in the present study, we evaluated the response to anti SARS-CoV-2 vaccination in a cohort of patients undergoing solid organ transplantation through the serological immunoglobulin assay and the evaluation of the immunosuppressiveant drug blood concentration.