Illustration of nanobodies (blue) binding to the receptor binding domain (RBD) of the SARS-CoV-2 coronavirus spike (S) protein (red). S proteins are found in the viral membrane, they bind to receptors on host cell membranes and facilitate the virus entry to the cell. Nanobodies (single-domain antibodies) bind to the virus and neutralise it, preventing it from causing infection. Nanobodies small molecular size relative to typical antibodies makes them suitable for delivery via aerosol. SARS-CoV-2 is the virus that causes the disease Covid-19, a respiratory illness.