5). vaccination for 135 participants without prior SARS-CoV-2 infection. Antibody titers and potency were assessed using three assays against SARS-CoV-2 proteins that bamlanivimab does not efficiently bind to, thereby reflecting the endogenous antibody response. All bamlanivimab and placebo recipients mounted a robust immune response to full COVID-19 vaccination, irrespective of age, risk-category, and vaccine type with any observed differences of uncertain clinical importance. These findings are pertinent for informing public health policy with results that suggest that the benefit of receiving COVID-19 vaccination at the earliest opportunity outweighs the minimal effect on the endogenous immune response due to prior prophylactic COVID-19 monoclonal antibody infusion. Individuals infused with an anti-SARS-CoV-2 antibody demonstrated a robust immune response to subsequent COVID-19 vaccination. == INTRODUCTION == In response to the coronavirus disease 2019 (COVID-19) pandemic, many prophylactic and therapeutic treatments were rapidly developed Rigosertib to target the highly pathogenic severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) (1,2). Antibodies that target the receptor binding domain (RBD) of the spike protein of SARS-CoV-2 are essential for protection against COVID-19 (3,4); these BIRC2 antibodies reduce SARS-CoV-2 viral load, which is correlated with disease severity (57). Active immunity against COVID-19 develops when endogenous RBD-neutralizing antibodies are elicited following exposure to a pathogenic agent, such as SARS-CoV-2 or a COVID-19 vaccine (3,4); passive immunity is conferred through the administration of exogenous antibodies, such as monoclonal antibodies (mAbs), that precisely target and bind to the RBD. Several clinically active COVID-19 mAbs provide immediate protective immunity that persists for as long as the antibody concentration exceeds that required for neutralization of the virus (812). Bamlanivimab was the first COVID-19 mAb to be granted Emergency Use Authorization (EUA) in November 2020 by the U.S. Food and Drug Administration (FDA), but was later revoked in April 2021 due to the increase of SARS-CoV-2 viral variants that were resistant to bamlanivimab alone (11,13). Vaccine-induced protection develops over time, often requiring multiple doses of vaccine, but offers clear advantages by eliciting a broader polyclonal immune response and establishing immunological memory for durable Rigosertib immunity (14,15). There are currently insufficient safety and efficacy data with COVID-19 vaccines Rigosertib in individuals who have previously received COVID-19 mAbs; in the absence of data, both the World Health Organization (WHO) and the Centers for Disease Control and Prevention (CDC) recommend the deferral of vaccination for 90 days following mAb treatment and more recently, if mAbs were received for post-exposure prophylaxis (PEP), the CDC now recommends vaccine deferral for Rigosertib 30 days (16,17). In order to avoid unnecessary delays for individuals seeking vaccination and to inform public health policy, it is critical that we understand any effect that therapeutic mAbs have on Rigosertib the subsequent vaccine-induced immune response. Vaccine efficacy against COVID-19 is correlated with the elicitation of antibodies, and accordingly serological assays are critical tools for monitoring the longitudinal endogenous antibody responses following COVID-19 treatments or SARS-CoV-2 infection (1820). In a prospective treatment case study, an individual who was treated with an anti-SARS-CoV-2 mAb for symptomatic SARS-CoV-2 infection and received mRNA COVID-19 vaccination more than 40 days thereafter, exhibited comparable post-vaccine antibody responses to SARS-CoV-2 RBD for SARS-CoV-2 variants (including Alpha, Beta, and Gamma), to other participants who had not received an anti-SARS-CoV-2 mAb and were vaccinated following confirmed SARS-CoV-2 infection (21). However, larger studies are required to assess the duration of exogenous anti-SARS-CoV-2 mAbs in individuals with COVID-19 and whether these mAbs interfere with a subsequent immune response to a later COVID-19 vaccine. Additional studies are also required to assess the potential impact of.