Abstract
Appropriately selected neutralising monoclonal antibodies (nmAbs) are an effective treatment for patients with mild or moderate coronavirus disease 2019 (COVID-19) who are at high risk of progression to severe disease. In contrast, the efficacy of nmAbs in patients hospitalised with COVID-19 has been mixed, and clinical benefit has largely been restricted to seronegative patients [i.e. those lacking endogenous severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibodies] in the trials with positive outcomes. This review summarises the major clinical trial data investigating nmAb treatment for hospitalised patients with COVID-19, and explores current definitions of seropositivity, what they mean in a late-pandemic context and discusses the current late-pandemic challenges associated with defining 'seroprotection' in a clinically meaningful way. We conclude that following widespread vaccination, increasing numbers of prior infections and emerging viral variants, seropositivity now reflects a range of immune coverage rather than a binary tool with which to aid decision-making on a clinically actionable timescale. Treatment decisions with nmAbs in a late-pandemic context would therefore likely best rely on information regarding clinical status, time since symptom onset, underlying patient condition(s) and the dominant circulating variant, should they be approved for future use in hospitalised patients with COVID-19.