Scientists have identified a pair of neutralizing antibodies - isolated from a patient who recovered from COVID-19 - that bind to the glycoprotein spike of the SARS-CoV-2 virus, blocking the spike's ability to bind to the human ACE2 receptor and mediate viral entry into host cells. Preliminary tests of the two antibodies in a mouse model resulted in a reduction of virus titers, suggesting that the antibodies may offer therapeutic benefits - in addition to informing the design of small molecule therapeutics and vaccine candidates to fight COVID-19. Yan Wu and colleagues found that the antibodies, named B38 and H4, can each bind simultaneously to different epitopes on the spike's receptor binding domain (RBD), such that both antibodies together may confer a stronger neutralizing effect than either antibody on its own - a prediction supported by in vitro experiments. This feature also means that, should one of the viral epitopes mutate in a way that prevents the binding of one of the two antibodies (a phenomenon known as immune escape), the other antibody may yet retain its neutralizing activity. By imaging the structure of the viral spike's RBD bound to B38, Wu et al. confirmed that B38 binds to a subset of the amino acids bound by ACE2 in the RBD, providing an explanation for why B38 confers such strong neutralizing effects. The authors suggest that a "cocktail" containing both antibodies could provide direct therapeutic benefits for COVID-19 patients, while the new information regarding the viral spike epitopes could aid the development of small molecule antivirals and vaccine candidates to fight the SARS-CoV-2 virus.