Writing on MedRxiv, they report that higher levels of anti-spike, anti-RBD IgG, and neutralising antibody titres were associated with a greater degree of protection against COVID-19 – defined as a PCR positive test with at least one symptom present. These data were then used to build a model to extrapolate the levels of antibody associated with varying degrees of protection, providing estimates for a range of vaccine efficacies from 50% to 90%, using three different assays. The study also confirms previous indications that there is no single level on any of the binding or neutralising antibody assays used, that provides full protection against COVID-19. The results link immune responses to expected population protection after 2 doses, but cannot be used to check protection of an individual who has been vaccinated or protection conferred by a single dose. Professor Sir Andrew Pollard, Director of the Oxford Vaccine Group, and Chief Investigator on the Oxford Vaccine Trial, said: ‘There
