There is a growing interest in using monoclonal antibodies (mAbs) in the early stages of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection to prevent disease progression. Little is known about the efficacy of mAbs against the delta variant of concern and its clinical presentations. We evaluated the effect of casirivimab/imdevimab treatment among five delta vaccine breakthrough patients. Symptomatic non-hospitalized vaccinated patients were submitted to nasopharyngeal swabs for the detection of SARS-CoV-2 and Next-Generation Sequencing (NGS). Blood analysis and chest Computed Tomography were also performed. A cocktail of casirivimab/imdevimab was administrated, and patients were monitored weekly. Clinical evolution was evaluated by the regression of the symptoms, negative results by real-time RT-PCR, and by the need of hospitalization: these aspects were considered as significant outcomes. In four cases, symptom reversion and viral load reduction were observed within 2 days and 7 days after mAbs treatment, respectively. Only one case, suffering from thymoma, was hospitalized 2 days later because of respiratory failure, which reverted within 18 days. mAbs treatment seems to be safe and effective against the delta variant and its clinical manifestations.

Neutralizing monoclonal antibodies (mAbs) for pre- and post-exposure prophylaxis of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) are largely used to prevent the progression of the disease by blocking viral attachment, host cell entry, and infectivity. Sotrovimab, like other available mAbs, has been developed against the receptor binding Domain of the Spike (S) glycoprotein of the virus. Nevertheless, the latest Omicron variant has shown marked mutations within the S gene, thus opening the question of the efficacy of these neutralizing molecules towards this novel variant. In the present observational study, we describe the effects of Sotrovimab in the treatment of 15 fully vaccinated patients, infected by SARS-CoV-2 Omicron sub-variants, who were selected on the basis of factors widely considered to affect a worse prognosis: immune suppression (n = 12) and/or chronic kidney disease (n = 5) with evidence of interstitial pneumonia in nine patients. The effectiveness of Sotrovimab in the treatment of severe cases of COVID-19 was demonstrated by the regression of symptoms (mean 5.7 days), no need of hospitalisation, improvement of general health conditions and viral clearance within 30 days in all patients. In conclusion, although loss or reduction of mAbs neutralizing activity against the Omicron variant have been described, Sotrovimab has clinically proven to be a safe and useful treatment for patients with high risk of progression to severe COVID-19 infected by Omicron sub-variants.