acknowledgement of the original source. These permissions are granted for free by Elsevier for as long as the COVID-19 resource centre remains active.

To the editor: Coronavirus disease 2019 (COVID-19) vaccines are efficient to prevent severe COVID-19 infections. Immunocompromised patients are at increased risk of both severe COVID-19 and poor immunologic response to antisevere acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccines.

Preexposure prophylaxis using anti-spike neutralizing monoclonal antibodies to prevent COVID-19 infection has been proposed as an alternative in patients with no immunologic response after 3 doses of COVID-19 vaccines. 1,2 We herein provide the first report, to our knowledge, of breakthrough COVID-19 infections in immunocompromised patients treated preventively with REGEN-Cov (Regeneron; casirivimab þ imdevimab).

Between September 24,