Participants were divided into two groups, one for individuals previously infected with SARS-CoV-2 and the other for individuals without previous infection. SARS-CoV-2 and the other for individuals without previous infection. The median IgGS titers decreased monthly both in previously infected individuals and in the uninfected group. Previously infected individuals had significantly higher median titers of IgGS compared with previously uninfected subjects at all seven time points after complete vaccination (< 0.001). Seven months after vaccination, the median IgGS titer had decreased by more than 92% both in individuals previously infected with SARS-CoV-2 and in uninfected individuals. However, IgGS antibodies were still detected in all Iodixanol study participants and persisted throughout the 7 months after the second dose of the vaccine. Further studies should be conducted to monitor the antibody response to the BNT162b2 mRNA vaccine beyond 7 months, to assess the need for a new booster dose in Iodixanol order to extend the duration and amplitude of the specific immune response. Keywords: SARS-CoV-2, antibodies, spike protein, COVID-19, vaccine, healthcare workers, Romania 1. Introduction Full immunization with two doses of the BNT162b2 mRNA COVID-19 vaccine (Pfizer-BioNTech) has been shown to have a consistent high efficacy (95%) [1,2], regardless of age, sex, race, or associated pathology, with or without evidence of previous severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection [3]. Vaccination success can now be confirmed based on the detection of specific antibodies against the receptor-binding domain of the S1 subunit of the spike protein, by using different assays: electrochemiluminescence sandwich immunoassay (ECLIA), chemiluminescence microparticle immunoassay (CMIA), chemiluminescence immunoassay (CLIA), or enzyme-linked immunosorbent assay (ELISA) [4]. However, comprehension regarding immunity to SARS-CoV-2 is limited [5], and the durability of immune responses after vaccination is currently unknown [6]. Several studies have reported on the antibody response in fully vaccinated individuals with a limited follow-up of the participants, i.e., below 7 months [7,8,9]. To evaluate the antibody kinetics in individuals vaccinated with a two-dose regimen of the BNT162b2 vaccine, a longer follow-up period is needed. This is important, especially to assess the need for a new booster Rabbit Polyclonal to PTRF dose in order to extend the duration and amplitude of the specific immune response. In this study, we evaluated the SARS-CoV-2 antibody response in healthcare workers who were vaccinated with the Pfizer-BioNTech mRNA vaccine two-dose regimen in Western Romania. The antibody response to the BNT162b2 mRNA COVID-19 vaccine was assessed monthly, for 7 months, in two groups: individuals previously infected with SARS-CoV-2 and individuals without previous infection. 2. Materials and Methods 2.1. Study Design and Population Ninety-seven fully vaccinated volunteers, residents of Timis County (705,113 inhabitants), Romania, were initially enrolled in this study. The individuals were all healthcare workers from the Municipal and County Clinical Emergency Teaching Hospitals in Timisoara, Romania. Five study participants (3 males and 2 females) were infected with SARS-CoV-2 in the first month after vaccination, confirmed by real-time polymerase chain reaction (RT-PCR), and were excluded from this study. Finally, 92 people were included in the study. Study participants were healthy adults, with no symptoms possibly related to infection in the 14 days prior to enrollment in the study. Of the 92 subjects, 33 had confirmed SARS-CoV-2 past infection, by RT-PCR and/or detection of SARS-CoV-2 anti-nucleocapsid (N) protein IgG (IgGN), and 59 subjects had not been infected with SARS-CoV-2. Previously SARS-CoV-2 infected and uninfected individuals were grouped into two age categories (24C44 years and 45C66 years). Serum samples of the 92 individuals were collected between February 26, 2021 and September 26, 2021. All Iodixanol study participants had been vaccinated with 2 doses of the BNT162b2 mRNA COVID-19 vaccine (Pfizer-BioNTech, Mainz, Germany), 21 days apart [1]. Each participant was tested monthly for 7 weeks, starting at one month after receiving the second dose of the vaccine. Samples were kept at C20 C until laboratory tests were performed in the Clinical Laboratory of the Municipal Clinical Emergency Hospital in Timisoara, a research laboratory for COVID-19 screening in Romania. Informed consent was from all subjects involved in the study. The Ethics Committee of the Municipal Clinical Emergency Teaching Hospital in Timisoara, Romania approved this study. 2.2. Serologic Checks The vaccine-elicited antibody response, SARS-CoV-2 anti-spike (S) protein IgG (IgGS), was recognized using the SARS-CoV-2 IgG II Quant assay (Abbott, Diagnostics Division, Sligo, Ireland), a chemiluminescent microparticle immunoassay (CMIA) having a level of sensitivity of 98.1% and specificity of 99.6% [10]. The assay was performed within the Abbott Alinity i system (Abbott Laboratories, Lake Bluff, IL, USA). Serum samples with cutoff 50.0 AU/mL were considered positive for IgGS [10]. To detect previous SARS-CoV-2 infections, serum SARS-CoV-2 anti-nucleocapsid.