Repeated measurements ANOVA with Greenhouse-Geisser correction followed by post hoc testing with Bonferroni correction were conducted to analyze antibody concentrations about day 0, day 3, and day 21. no influence on the final outcome of the booster vaccination. Before booster vaccination, antibody concentrations were lower for older participants but improved more strongly over time. Keywords:SARS-CoV-2, booster, third vaccination, BNT162b2, ChAdOx1-nCoV-19, T cell response, antibody concentration == 1. Intro == The distributing of the SARS-CoV-2 Omicron variant has been raising concerns because of its high transmissibility and its potential to infect those previously vaccinated [1,2]. In Germany, due to the declining safety of the BNT162b2 vaccination over time, a third vaccination dose (booster) has been recommended to counter the rapid spread of the Delta and Omicron variants. Booster vaccinations have been associated with reduced COVID-19 mortality [3,4], and have been demonstrated to increase anti-S antibody concentration and neutralizing antibody concentrations, which ADAM8 are highly predictive of safety from symptomatic illness [5], by a factor of 4 to 73 [6]. Moreover, SARS-CoV-2 spike-specific T cell reactions are considerably improved in booster recipients [6]. At the beginning of the vaccination marketing campaign, due to a shortage of vaccines and uncertainties concerning side effects, most German residents received either two doses of BNT162b2 (homologous vaccination) or priming with ChAdOx1-nCoV-19, followed by OPC21268 a second vaccination with BNT162b2 (heterologous vaccination). Studies emphasize the improved effectiveness of a heterologous vaccination routine compared with a homologous vaccination with regard to the antibody concentration after vaccination [7,8,9,10]. Both vaccination regimens induce CD4+and CD8+T cells reactive to SARS-CoV-2 S-protein peptides [11,12,13]. Studies suggest that these T cells display reactivity against SARS-CoV-2 variants [11,14]. In this study, we aimed to investigate the effect of the previous vaccination routine (heterologous or homologous vaccination) on a third vaccination with BNT162b2 with respect to antibody concentrations and IFN production by T cells. Here, we statement the results of the 1st five weeks of the application observation. == 2. Materials and Methods == == 2.1. Study Population == The application observation started in December 2021. Participants (n = 75) were recruited from among healthcare employees of the hospital Sonnenblick in Marburg, OPC21268 Germany. All employees of the hospital who received a third vaccination with BNT162b2 (Comirnaty, BioNTech/Pfizer, Mainz, Germany/New York, NY, USA) and were willing to participate were included (Table 1). There were no exclusion criteria. == Table 1. == Participants characteristics. Age and gender were recorded. Previous OPC21268 illness: Either positive PCR test result or anti-N antibodies positive. Out of 75 participants, n = 19 were included for the measurement of antibody concentration and T cell response after 7 and 35 days. Abdominal: antibody concentration (U/mL). Heterologous vaccination: ChAdOx1-nCoV-19 and BNT162b2. Homologous vaccination: BNT162b2 and BNT162b2. IQR: Interquartile range. The age and gender of each participant were recorded as well as information about the first and second vaccination (day and vaccine) and known illness with SARS-CoV-2. Within the platform of quality assurance in the hospital, all employees were previously given the chance to measure the antibody concentration with the same assay as used in the course of this software observation after the second vaccination. The data from your measurement of n = 46 participants were available. In total, the number of study participants amounted to n = 75, aged 2163 years. N = 15 males and OPC21268 n = 60 ladies participated in the study. All participants received their 1st and second vaccination between May and June 2021. N = 20 participants were vaccinated with two doses of BNT162b2 (homologous), while n = 53 participants received a priming dose of ChAdOx1-nCoV-19 (Vaxzevria, AstraZeneca, Cambridge, UK) followed by a second dose of BNT162b2 (heterologous). Two participants received only one dose of BNT162b2 because of previous SARS-CoV-2 illness (positive PCR test result). One participant remaining the study after day time 0, one missed day time 21, and another remaining before day time 35. N = 4 participants did not continue after day time 7. The study was authorized as an application observation from the Paul-Ehrlich-Institute (NIS-No. 642) relating to 4 (23) phrase 3 of the German Medicines Act. Informed consent was from OPC21268 all participants. == 2.2. Antibody Assay == For antibody measurement, venous blood samples were collected before booster vaccination as well as 3 days and 3 weeks after the booster. For any subset of n = 19 participants, concentrations were also measured 1 and 5.