reported that this median IgG anti-S-RBD levels were increased after full vaccination with BNT/BNT and ChAd/BNT[21]

reported that this median IgG anti-S-RBD levels were increased after full vaccination with BNT/BNT and ChAd/BNT[21]. binding were tested. == Results == In the BNT162b2 vaccine group, total antibody against SARS-CoV-2 remained constant until 6 months, while the other vaccine groups showed a significant decrease, as compared to the unvaccinated group. The level of anti-SARS-CoV-2 S-RBD protein IgG was significantly increased in the ChAdOx1 n-CoV-19, Gam-COVID-Vac, and BNT162b2 vaccines I-191 groups as compared to the unvaccinated group. Participants in the BNT162b2 vaccine group had higher ACE2 inhibition efficiency compared to the other vaccine groups as well as the unvaccinated group. == Conclusions == The BNT162b2 vaccine showed the highest level of antibody against SARS-CoV-2, followed by the BBIBP-CorV, Gam-COVID-Vac, and ChAdOx1 n-CoV-19 vaccines. The level I-191 of antibodies was increased in people infected with SARS-CoV-2 after vaccination, as compared to uninfected but vaccinated individuals. Keywords:COVID-19, Vaccine, Antibody response, Binding inhibition, Severity == 1. Introduction == Coronavirus disease 2019 (COVID-19), caused by infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), was first reported in Hubei Province, People’s Republic of China at the end of December 2019 and then spread rapidly around the world[1],[2],[3],[4],[5]. Mongolia reported the first local transmission in November 2020[6]and started a nationwide vaccination program against COVID-19 in March 2021. COVID-19 vaccines including BNT162b2 (Pfizer/BioNTech), mRNA-1273 (Moderna), ChAdOx1 n-CoV-19 (AstraZeneca), Gam-COVID-Vac (Sputnik V), and BBIBP-CorV (Vero cell) have been shown to reduce hospitalization and mortality rates [6,7]. Studies have reported that neutralizing antibodies against SARS-CoV-2 virus show protection from this infection[8]. The reported seroprevalence of SARS-CoV-2 infection has varied across different regions including Southeast Asia, Africa, the Eastern Mediterranean, America, and Western Pacific, with rates ranging from 1.7% to 19.6%[9]. A national population survey published in 2021 reported a seroprevalence of around 1.45% in Mongolia[10]. Studies have reported the antibody response after vaccination with the COVID-19 vaccines. A study conducted by Dashdorj et al. tested the antibody responses to four I-191 types of vaccine TGFBR2 available in Mongolia at around 8090 days after the second dose of vaccine in July 2021[11]and showed the Pfizer/BioNTech vaccine to have the highest blocking activity of receptor binding domain (RBD)angiotensin-converting enzyme receptor 2 (ACE2), followed by the AstraZeneca vaccine, then Sputnik V and Sinopharm[11]. Evaluating the titer of antibodies against SARS-CoV-2 infection before the third dose or after the full two doses of COVID-19 vaccines is essential for virus containment and vaccine choice. This study was performed to compare the levels of antibodies against N and S1 RBD, as well as the antibody inhibiting RBDACE2 binding, of four different vaccines at 6 months after the second dose in Mongolia: BNT162b2 (Pfizer/BioNTech), ChAdOx1 n-CoV-19 (AstraZeneca), Gam-COVID-Vac (Sputnik V), and BBIBP-CorV (Vero cell). == 2. Participants and methods == == 2.1. Study participants == Two hundred individuals without SARS-CoV-2 infection who had received two doses of vaccine were included in the vaccine groups (50 in each group: BBIBP-CorV, ChAdOx1 n-CoV-19, Gam-COVID-Vac, and BNT162b2), and two hundred individuals who had been infected with SARS-CoV-2 infection 28-64 days after vaccination were included in vaccine plus SARS-CoV-2 infection groups (50 in each group: BBIBP-CorV+COVID-19, ChAdOx1 n-CoV-19+COVID-19, Gam-COVID-Vac+COVID-19, and BNT162b2+COVID-19) and 50 individuals who had previously been infected with SARS-CoV-2 were included in the unvaccinated group. A study to determine SARS-CoV-2 antibodies was conducted 6 months after the second vaccine dose, from October 18, 2021 to January 5, 2022 in Mongolia. All participants provided I-191 written informed consent. People who refused to participate, those who had only received the first vaccine dose, and people who had only recently received their second dose of vaccine were excluded from this study. Ethical approval was obtained from the research ethics review boards of the Ministry of Health of.