Generally, policy decisions regarding the dosing regimens consider the current prevalence of SARS-CoV-2 infection, which variants of concern are emerging, population susceptibility, and vaccine supply. in na?ve participants at 8C12 weeks post first dose were comparable to the GMT (1674.94) observed in P.I. participants prior to vaccination. Interestingly, P.I. participants had significantly higher antibody titers compared to na?ve participants, after both the first (GMT, 4913.50 vs. 1632.16) and second doses (GMT, 9804.60 vs. 6607.30). Taken together, our findings show that a single ChAdOx1 nCoV-19 dose in previously SARS-CoV-2 infected individuals elicits comparable, if not higher, antibody responses to those of two-dose-vaccinated na?ve individuals. Keywords: ChAdOx1 nCoV-19, SARS-CoV-2, vaccine, dose, RBD, na?ve, prior contamination 1. Introduction Due to a wide variety of viral strains belonging FR 180204 to the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) type, coronavirus disease 2019 (COVID-19) causes a broad spectrum of diseases primarily affecting the respiratory and vascular systems of the human body. The SARS-CoV-2 viral strains can be highly transmittable, pathogenic, or capable of evading the adaptive immune responses. SARS-CoV-2 human-to-human transmission occurs mainly through exposure to respiratory fluids carrying infectious virus. COVID-19 continues to be a major public health concern, causing severe illness and deaths in Ethiopia and the rest of the world alike. Mass vaccination against SARS-CoV-2 is the most effective public health intervention to protect against morbidity and mortality related to SARS-CoV-2 contamination [1]. Safe, efficacious, and licensed COVID-19 vaccines, including ChAdOx1 nCoV-19 (AZD1222; OxfordCAstraZeneca), are available [2,3,4,5], despite being challenged by the recurrent emergence of new SARS-CoV-2 variants. Real-world vaccine efficacy studies from developed countries have shown that the current vaccines are able to generate effective humoral and cellular immunity, albeit differential responses are observed between vaccine-induced immunity and hybrid (vaccine-induced immunity combined with natural contamination) immunity [6,7]. Several correlates of protection studies have exhibited that higher antibody titers are associated with decreased risk of subsequent symptomatic SARS-CoV-2 contamination [8,9,10,11,12], and several studies from developed countries have revealed the rapid waning of antibody levels among SARS-CoV-2-infection-na?ve vaccine recipients compared to those individuals with hybrid immunity [7,13,14,15,16]. Despite the importance of immune sturdiness data for guiding national vaccination strategies, there is a dearth of studies from Ethiopia and other African countries looking at more locally relevant populations. The ChAdOx1 nCoV-19 vaccine utilizes a replication-deficient adenoviral vector that induces expression of SARS-CoV-2 spike (S) protein in host cells, particularly in the skeletal muscle [17]. Vaccinated individuals subsequently generate antibodies against the spike protein, including those that target the receptor-binding domain name (RBD), which contains many neutralizing epitopes. However, they do not generate antibodies against other SARS-CoV-2 structural and non-structural proteins, such as nucleocapsid (N) [18]. Studies have shown a strong correlation between anti-RBD IgG titers and SARS-CoV-2 neutralizing titers [15]. Therefore, Rabbit Polyclonal to PHLDA3 in resource-limited countries, it is FR 180204 advantageous to use anti-RBD IgG testing as a proxy for virus neutralization to assess the protection offered by the ChAdOx1 nCoV-19 vaccine. As part of the strategy to evaluate the Ethiopian national COVID-19 response through vaccination, we established a longitudinal cohort of healthcare professionals working at the Armauer Hansen Research Institute (AHRI), with and without evidence of prior SARS-CoV-2 contamination and decided their levels of ChAdOx1 nCoV-19 vaccine-induced anti-RBD IgG titers across two-time points. The present study generated evidence of the durations of ChAdOx1 nCoV-19 vaccine-induced humoral responses and the long-term effects of prior SARS-CoV-2 contamination on subsequent vaccine-induced responses. 2. Materials and Methods 2.1. Study Design and Participants We conducted a longitudinal prospective study constituting healthcare professionals from AHRI, who were also one of the priority target recipients of the ChAdOx1 nCoV-19 vaccine. Vaccination was offered through the Ethiopian Ministry of Healths national COVID-19 vaccination campaign. In this analysis, only FR 180204 participants who were vaccinated with the ChAdOx1 nCoV-19 vaccine were included. About 5 mL of venous blood was collected from a total of 63 (= 27 female and = 36 male) participants, aged 24C59 years (mean of 38.1 standard deviation of 8.36) before vaccination and in two subsequent post-vaccination follow-ups (Figure 1) to monitor humoral responses to the vaccine. The first (hereafter designated as 1d + 8C12w) was conducted at 8C12-weeks after the first dose, whereas the second follow-up (designated hereafter as 2d + 8C12w) was done 8C12 weeks after the second dose (Figure 1). All participants received their first dose between 23 March 2021 and 31 March 2021. The interval between the first and the second doses was 12 weeks (range 83C97.