Reliance on immunity from prior infection is not secure for hospital infection control

Abstract There has been much discussion on the general principle of "naturally-acquired” immunity arising from recovery from SARS CoV 2infection, and this recovery state contributing to the prevalence of immunity to reinfection, often referred to as Herd Immunity. This has led to the belief that hospital staff previously infected are safe and do not require vaccine. We demonstrate here that this may be a misplaced notion because the avidity with which the antibody from a person recovered from corona virus infection, even if of a high titre, is low. Effete antibody of low avidity is, therefore, unlikely to impact on the incidence of infection in the population, or indeed protect the individual. By contrast, a single immunisation of a previously-recovered individual by vaccine significantly increases the antibody avidity.