Although in vitro studies suggest that neutralization by monoclonal antibodies (mAbs) against SARS CoV2 Omicron sub lineages is reduced, in vivo virological response data are lacking. MONET (EudraCT: 2021-004188-28) was multi-centric phase 4 open-label parallel randomized clinical trial, conducted in Italy over 2022-2023, to assess the efficacy of sotrovimab (SOT), tixagevimab/cilgavimab (TIX/CIL) and Nirmatrelvir/ritonavir (NMV/r), in outpatients at high risk for severe COVID-19. The outcome (secondary in the trial protocol) was SARS-CoV-2 variation in cycle threshold (CT) values over the first 7 days (D1-D7) of the trial. CT variation was compared by trial arms using unadjusted linear regression and after controlling for age. We included 346 individuals: 116 (34%) received SOT, 113 (33%) TIX/CIL, 117 (34%) NMV/r. Main characteristics were balanced across arms. Most of the participants were infected with BA.2 (52%) or BA.4/5 (35.5%). The data carried strong evidence that the mean CT change over D1-D7 was larger in subjects receiving NMV/r vs. the other arms (p < 0.001). We found no evidence that viral variant was an effect measure modifier for the contrasts of interest (p = 0.14). Our analysis provides strong evidence that NMV/r exerts a greater in vivo antiviral effect than anti-Spike mAbs against Omicron sub lineages, confirming previous in vitro data.
