Investigation of severe acute respiratory syndrome coronavirus 2 infection status in solid organ transplant recipients treated with tixagevimab/cilgavimab

Introduction Tixagevimab and cilgavimab (T/C) are neutralizing antibodies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that can be used to prevent SARS-CoV-2 infection in solid organ transplant (SOT) recipients. However, their neutralizing activity against recent variants was reduced, raising concerns regarding the emergence of breakthrough coronavirus diseases 2019 (COVID-19). This study aimed to investigate the status of the COVID-19 breakthrough after T/C administration. Methods We retrospectively investigated breakthrough COVID-19 in SOT recipients administered T/C at Kyoto University Hospital, Japan, from November 2022 to March 2023. Patients were monitored for 6 months after T/C administration. SARS-CoV-2 infection was diagnosed using polymerase chain reaction or antigen tests. The monthly incidence rates of SARS-CoV-2 infection were calculated using the person–time method. Results T/C were administered to 67 SOT recipients (liver, 16; lung, 36; and kidney, 15), of whom five were infected with SARS-CoV-2. All five cases were classified as mild, and none of these patients required admission to the intensive care unit (ICU) or died. All infected individuals tested positive for SARS-CoV-2 after March 2023, when T/C-resistant subvariant strains became predominant. The monthly incidence rate of SARS-CoV-2 infection, calculated using the person–time method, suggested an increasing trend. Conclusions During the T/C-resistant variant epidemic, SARS-CoV-2 infections were identified even after T/C administration, suggesting that the prophylactic effects of T/C were invalid. Therefore, emerging variants must be carefully monitored and characterized to determine appropriate antiviral strategies, such as the use of suitable neutralizing antibodies.