Thus, anti-RBD IgG antibody levels are used to assess a level of safety [17,18,19]. Written educated consent was received by all participants. = 481, 77.2%). A total of 94.2% participants had received two doses of vaccines (n = 587) and 12.4% (n = 720) had been infected at least once. Most common prime-boost routine was BNT162b2 + BNT162b2 (57.9%, n = 361). Age (p< 0.001), days since vaccination (p= 0.007), and the homologous vaccination routine with ChAdOx + ChAdOx (p= 0.004) were risk factors for the antibody level being below the CoP, whereas any previous COVID-19 illness (p< 0.001), the number of vaccines (p= 0.016), and physical issues after vaccination (p= 0.01) were CR2 associated with an antibody level above the CoP. Therefore, age, vaccination routine, days since vaccination, and earlier illness influence the antibody level. These risk factors should be considered for booster and vaccinations recommendations. Keywords:SARS-CoV-2, vaccinations, healthcare workers, public health, COVID-19 == 1. Intro == At the beginning of the pandemic and before vaccination programs were implemented, SARS-CoV-2 was able to hit an immunological nave human population, resulting in a fast spread around the globe with severe results. Since late 2020, vaccinations against the novel SARS-CoV-2 have been available and early studies showed an initial adequate vaccination effectiveness [1]. However, new variants such as the Delta variant (B.1.617.2) and subsequent variants became able to escape immune acknowledgement and led to increased reports of vaccine breakthroughs [2,3]. To measure vaccine effectiveness through the amount of antibodies, there are different quantitative assays that Midecamycin are used in the medical setting. Some assays measure the quantity of neutralizing antibodies in IU/mL. Additional assays calculate the ligand binding antibody devices against SARS-CoV-2 spike protein or receptor binding website (RBD), either as arbitrary devices (AU/mL) or, after adjustment to the WHO standard, as binding antibody devices (BAU/mL) [4]. However, the exact level of vaccine-induced antibody response that prevents illness (correlate of safety, CoP) is still pending. A hurdle in the dedication of a popular CoP lies within the non-standardized assays globally used to detect serum antibody levels. Additionally, the immune defense against SARS-CoV-2 takes place through a complex interplay of cellular and humoral factors. Besides antibodies, the cellular immune response by SARS-CoV-2-specific T-lymphocytes plays an important part [5,6], which makes it hard to forecast the immune response based on a defined threshold alone. Measurement of antibodies is definitely widely used and approved, as the cellular immune reactions are theoretically hard to measure. Besides a definitive CoP in order to classify vaccine effectiveness, it is important to know what potential factors may influence the antibody level. It is known that Midecamycin not only the different types of Midecamycin vaccines (e.g., inactivated, live-attenuated, toxoid) and time since vaccination can alter the immune response, but also intrinsic sponsor factors such as comorbidities (e.g., obesity, tumor, cardiovascular, and autoimmune or chronic diseases) influence the immune response to vaccination [7,8,9]. Age is an important factor, as individuals have a lower vaccine response in the extremes of age groups of existence. Neonates have a less strong antibody production; the elderly, for example, possess a more quick antibody waning and a decrease in antibody response to Midecamycin vaccinations [7,9]. Gender can also influence the antibody response; females are known to build a stronger and longer-lasting vaccine response than males due to genetic and hormonal variations [7,10,11]. At the same time, females have been shown to statement more adverse effects following vaccination than males [7,12,13]. These factors are known to alter the antibody level after known vaccinations, but it is not fully known if it also applies for the COVID-19 vaccines. Prior studies examined reactogenicity and immunogenicity of vaccines among healthcare workers but focused on either side effects or serological antibody response [2,14]. Thus, our aim is usually to examine the antibody titer in vaccinated healthcare workers with possible associations to age, gender, time since vaccination, adverse reactions, and type of vaccine. == 2. Materials and Methods == == 2.1. Patient Selection and Data Collection == On 22 September 2021, all employees (approximately 1400 persons) of the Evangelische Kliniken in Gelsenkirchen, Germany with a personal email address received an invitation for a free assessment of their antibody titer through a blood sample. To reach employees with no personal email address, the Midecamycin invitation was posted on the hospitals intranet top news page; additionally, it was printed and displayed in prominent areas of the hospital. The letter included a questionnaire in which participants were asked to total if were participating. Participation was restricted to employees of the Evangelische Kliniken. Employees who, according to their questionnaire, experienced no history of vaccination still received antibody screening, but were not included in the study cohort. For antibody analysis, we used the fully automated access SARS-CoV-2-IgG.