Serological Profile of SARS-CoV-2 in Unvaccinated Blood Donors: A Nationwide Study During the Fifth Wave of the Pandemic in Iran

Background: Serological studies can demonstrate pathogen circulation in regional populations and reflect public health measures' effectiveness during different pandemic phases. By late November 2021, coinciding with the third pandemic wave, the seroprevalence of SARS-CoV-2 spike IgG antibodies among the Iranian population was 32.63%. Objectives: This study aimed to assess the Iranian population's seroprevalence during the fifth pandemic wave by analyzing donated blood samples. Methods: This population-based cross-sectional study was conducted on Iranian blood donors referred to all 31 main provincial capitals between August 2021 and September 2021. The participants selected through quota sampling were asked to complete a questionnaire on socio-demographics and coronavirus disease 2019 (COVID-19)-related information. Also, SARS-CoV-2 spike IgG antibodies were measured in serum samples using SARS-CoV-2 enzyme-linked immunosorbent assay (ELISA) kits. The seroprevalence was weighted based on the gender and age groups of the population and then adjusted for test performance. Results: Totally 3,339 blood donors participated in this study. The overall population-weighted seroprevalence adjusted for test performance was 52.67% (95% confidence interval (CI): 50.14 - 55.21). Seroprevalence was higher among participants with a high school diploma (55.45%, 95% CI 50.61 - 60.29), a positive history of close contact with COVID-19 patients (65.23%, 95% CI 60.83 - 69.63), and previous positive COVID-19 PCR tests (86.51%, 95% CI 82.32 - 90.7). Conclusions: More than half of the study population was exposed to SARS-CoV-2, indicating a 1.7-fold increase in the seroprevalence between late November 2020 and mid-September 2021. Our finding illuminated the pattern of Iran's fifth wave of the pandemic.