The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which causes COVID-19, has now spread all over the globe, infected millions, and already killed more than 200.000 people. Elderly people are most likely to develop severe disease and to die from COVID-19. The aim of this project is to have a manufacturable, cost-effective, ultrapotent SARS-CoV-2-neutralizing antibody ready for prophylactic use in the most vulnerable individuals by May 2021. This biologic will be subcutaneously injectable and fill the gap where, yet to come, COVID-19 vaccines may fail or perform poorly, i.e. in elderly individuals. The antibody will comprise a single domain antibody (also known as a nanobody) that targets the most vulnerable site in the viral spike protein. This nanobody building block will be fused to a human IgG1 Fc domain that carries half-life extension mutations, an alteration that has already been introduced in a multitude of clinically approved antibody-based biologics. Moreover, we will demonstrate high yield manufacturability of this SARS-CoV-2 neutralizing biologic in Chinese hamster ovary (CHO) cells (the gold standard production system), develop a downstream protein purification protocol, and demonstrate stability and antiviral potency in vitro and in vivo, in the highly relevant hamster model.