In this study we aim to characterize SARS CoV-2 strain specific immune response (SARS-CoV-2 Spike IgG) in health care workers and general populations at the Jimma Medical Center and the St. Paul Hospital in Addis Ababa in association to clinical immune protection and Covid-19 disease. Participants, stratified by SARS-CoV-2 infection and vaccination status, will be followed at 3-month intervals for a maximum of 2 years. Prevalence, incidence, and dynamics of SARS-CoV-2 specific antibodies as well as clinical assessments especially related to COVID-19 breakthrough disease in previously exposed/vaccinated participants will be performed. From a subset of selected participant blood sample, more in depth immunological analysis will be performed that include virus culture-based neutralization assays, antibody avidity assays, SARS-CoV-2 specific antibody epitope recognition using peptide arrays, and T-cell immunity assays (IGRA). We also plan to analyze and model cost-effectiveness considerations related to adapted COVID-19 vaccine strategies, specifically if SARS-CoV-2 the costs for routine sero-diagnosis in high SARS-CoV-2 prevalent population prior to vaccination will impact the decision to vaccinate (no vaccination for low-risk populations or reduced vaccine dosing) and is cost-efficient. The study is largely exploratory, providing deeper insights in SARS-CoV-2 specific immune responses and interaction with SARS-CoV-2 viral variants.