Fighting zoonotic coronaviruses In the past 20 years, three betacoronaviruses thought to have originated in bats have caused devastating disease in humans. The global pandemic caused by the latest such virus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), highlights the need to protect against other strains that could present a threat to humans. Cohen et al. constructed nanoparticles displaying the protein domain that binds the host cell receptor (receptor-binding domain or RBD), either a homotypic SARS-CoV-2 particle or mosaic particles displaying RBDs from four or eight different betacoronaviruses. In mice, antibodies to the SARS-CoV-2 RBD were elicited just as well by mosaic particles as by homotypic nanoparticles. The mosaic nanoparticles elicited antibodies that, beyond recognizing the strains displayed, also recognized mismatched strains. Science , this issue p. 735