Prior studies have shown that prior to the pandemic, Sierra Leoneans had more frequent exposures than Americans to coronaviruses with epitopes that cross-react with severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), SARS-CoV, and Middle Eastern respiratory syndrome coronavirus (MERS-CoV). Prior exposure to coronaviruses that induce cross-protective immunity may contribute to the greatly reduced incidence of COVID-19 cases and deaths in Sierra Leone compared to the United States. This supplement will (1) define the humoral immune response of Sierra Leoneans that may protect against infection with SARS-CoV-2 through isolation and characterization of pre-pandemic monoclonal antibodies, (2) develop diagnostic tests for novel coronaviruses and (3) determine the protective responses of cross neutralizing monoclonal antibodies in a nonhuman primate COVID-19 model.