The test is semiquantitative, corresponds to mRNA vaccine antigens, and is consistently correlated with neutralizing immunity. patients with previous contamination, the median levels of SARS-CoV-2 anti-S antibodies were BIBF0775 7,516 U/mL and 17,495 U/mL for those treated with BNT162b2 or mRNA-1273, respectively (p = 0.005). The Charlson comorbidity index (CCI) was significantly associated with protective levels of anti-spike IgG, with 3.6% of low- or non-responders using a CCI of 24 versus 18.9% in those with a CCI of 8 or more. The adjusted OR of developing a sufficient antibody level between the two vaccines was 3.91 (p = 0.0766) in favor of mRNA-1273. == Conclusions == Both of the evaluated mRNA-based vaccines for SARS-CoV-2 showed good efficacy. Preliminary data may data suggest a higher antibody response to the mRNA-1273 vaccine. == Graphical abstract == Keywords:SARS-Cov-2 vaccination, mRNA-based SARS-Cov-2 vaccine, Hemodialysis patients, Humoral response == Introduction == The first cases of coronavirus disease 2019 (Covid-19) were detected in Wuhan, China, in December 2019. Since the first onset of the illness it has spread to millions of people worldwide. Finally, the WHO declared the pandemic status. This disease BIBF0775 is usually characterized by high mortality among the elderly and patients with pre-existing morbid conditions. Innate immunity is usually a defense mechanism for immediate response to a variety of stimuli, including viruses. It consists of the activation and participation of pre-existing mechanisms, involving (the monocyte subsets) natural killer cells and natural killer T cells. In end-stage renal disease the -cell counts of both are diminished, indicating innate immune-system dysregulation [1]. In addition, patients on hemodialysis have a higher risk of contamination for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) due to comorbidities, as well as to CANPml limited capacity to respect rigid interpersonal distancing. In fact, they often travel to and from the dialysis unit by common transportation, they undergo a 3-session per week schedule in rooms with BIBF0775 many other patients, and they may have to spend time in the waiting room of the dialysis unit. In hemodialysis patients, who are usually affected by several comorbidities, Covid-19 is usually associated with higher morbidity and mortality [2], as occurred in 2009 2009 with the influenza A(H1N1)v pandemic in Latin America [3]. For these reasons, patients on dialysis were prioritized for vaccination in many countries, including Romania [4]. Finally, patients with advanced chronic renal insufficiency, and especially those on dialysis, are known to have a reduced immune response to vaccinations [5]. Nevertheless, the possible hyporesponsiveness to vaccines due to reduced innate and adaptive immune systems should not prevent patients on dialysis from receiving vaccination [6]. Higher vaccine dosage or scheduling changes were required in patients with Hepatitis B [7]. In an attempt to gain control of the pandemic, several vaccines were developed and approved within a very few months. Nonetheless, live attenuated vaccines should be avoided in patients on hemodialysis because of their dysregulated immune system. In Romania, both the mRNA Covid-19 vaccines BNT162b2 [8] and mRNA-1273 [9] were available for patients on hemodialysis. However, the pivotal trials that exhibited 9495% protection against Covid-19 contamination following a 2-dose regimen of the BNT162b2 or mRNA-1273 vaccine did not report data concerning patients on maintenance hemodialysis [8,9]. Actually, the Pfizer BiONTech trial of the BNT162b2 vaccine included 256 patients with renal disease but no further details on the stages of chronic kidney disease were reported [8]. A novel vaccine candidate (NVX-CoV2373) in a newly initiated phase III trial is usually prioritizing the enrollment of patients with underlying medical conditions including CKD [10]. Of course, results will come in due time. A recent review [11] reported 9 studies comparing the effectiveness of Covid-19 vaccinations. Altogether, 853 patients on maintenance dialysis (range 22154) were compared to 465 controls (range 7132). Ninety-eight point two% of patients were treated with BNT162b2, only 12 of whom, as reported by Lesny et al. [12], received a viral vector-based vaccine (AZD1222). Due to the paucity of evidence around the response to the standard protocol for mRNA Covid-19 vaccines, the aim of our study was to evaluate the level of antibodies against SARS-CoV-2 in patients on hemodialysis treated with two different mRNA-based vaccines. == Patients and methods == == Study design == In the five Renal Care Centers participating in the study, periodic screening of all patients has been performed every 2 weeks, irrespective of symptoms, since April 2020. This was the policy set by health authorities. More in detail, the diagnosis of SARS-CoV-2 contamination was confirmed by polymerase chain reaction (PCR) testing of nasopharyngeal swabs, processed.