Molecular model of nanobodies (yellow) binding to the receptor binding domain (RBD, pink) of the SARS-CoV-2 coronavirus spike (S) protein (blue). S proteins are found in the viral membrane, they bind to receptors on host cell membranes and facilitate the virus's entry to the cell. These nanobodies, developed from llama antibodies, bind to the virus and neutralise it, preventing it from causing infection. SARS-CoV-2 emerged in Wuhan, China, in December 2019. The virus causes the disease Covid-19, a respiratory illness that can lead to pneumonia and can be fatal in some cases.