![]() Ī total of 270 individuals were enrolled in the study from December 2020 to November 2021. Although studies suggest that vaccines can protect against severe COVID-19 from circulating variants of concern, the effectiveness of currently used vaccines against them is under evaluation. Part of the success of vaccines is also the ability to prevent and protect against infection from new variants that may be more virulent, pathogenic, or capable of avoiding immunity due to mutations on S protein. The produced neutralizing antibodies are associated with epitopes of the S protein, and it was found, in the serum of patients after COVID-19, that the RBD region was the primary target of these antibodies. The desired outcome for COVID-19 vaccines is to produce antibodies that will prevent the entrance of the virus into the host cell, thereby inhibiting its replication. Thus, most of them are either based on the S protein or on its immunogenetic region. Therefore, the S protein was considered as a competent immunodominant target for most SARS-CoV-2 vaccines. Vaccines developed for SARS-CoV-1 and MERS-CoV were based on protein S-inducing neutralizing antibodies with a protective effect. Patients after COVID-19 develop anti-S antibodies with neutralizing activity. In addition, protein S plays an important role in the host’s immune response due to its high antigenicity and ability to induce immune response. The S protein, especially the receptor-binding domain (RBD) of its S1 subunit, is crucial for virus entry into host cells through binding to human angiotensin-converting enzyme 2 receptor (ACE2) that is located on cell membranes. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) which causes COVID-19 is a positive-stranded RNA virus, and its genome includes multiple regions encoding nonstructural, accessory, and structural proteins such as spike (S), membrane (M), nucleocapsid (N), and envelope (E) proteins. Our results provide useful information regarding antibody responses after vaccination with different vaccine platforms, which can be useful for public health vaccination strategies. Lastly, all vaccine platforms had limited side-effects, with the most frequent pain at the injection site. Moreover, we identify that IgG and IgA responses depended primarily on both history of previous COVID-19 infection and vaccination platform used, with individuals immunized with a single-dose vaccine having lower antibody titers over time. We demonstrate that both mRNA and adenovirus vector-based vaccines caused mild side-effects and were effective in inducing adequate antibody responses against SARS-CoV-2, although BNT162b2 was superior concerning the intensity of antibody responses and protection against severe COVID-19. Antibodies were quantified by chemiluminescent microplate and ELISA assays. Serum sampling was performed on all participants on days 21, 42, 90, and 180 following the first dose, to evaluate anti-spike IgG and IgA responses. A total of 270 individuals were enrolled, of which 135 were vaccinated with adenovirus vector-based vaccines and compared with 135 age- and sex-matched participants who received the BNT162b2 mRNA vaccine. The aim of the study was to compare mRNA vaccine BNT162b2 with adenovirus vector- based vaccines in terms of presence of adverse reactions, immunogenicity, and protection against COVID-19.
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