Efficacy and Safety of Ensovibep for Adults Hospitalized With COVID-19 : A Randomized Controlled Trial

Ann Intern Med. 2022 Sep;175(9):1266-1274. doi: 10.7326/M22-1503. Epub 2022 Aug 9.


Background: Ensovibep (MP0420) is a designed ankyrin repeat protein, a novel class of engineered proteins, under investigation as a treatment of SARS-CoV-2 infection.

Objective: To investigate if ensovibep, in addition to remdesivir and other standard care, improves clinical outcomes among patients hospitalized with COVID-19 compared with standard care alone.

Design: Double-blind, randomized, placebo-controlled, clinical trial. (ClinicalTrials.gov: NCT04501978).

Setting: Multinational, multicenter trial.

Participants: Adults hospitalized with COVID-19.

Intervention: Intravenous ensovibep, 600 mg, or placebo.

Measurements: Ensovibep was assessed for early futility on the basis of pulmonary ordinal scores at day 5. The primary outcome was time to sustained recovery through day 90, defined as 14 consecutive days at home or place of usual residence after hospital discharge. A composite safety outcome that included death, serious adverse events, end-organ disease, and serious infections was assessed through day 90.

Results: An independent data and safety monitoring board recommended that enrollment be halted for early futility after 485 patients were randomly assigned and received an infusion of ensovibep (n = 247) or placebo (n = 238). The odds ratio (OR) for a more favorable pulmonary outcome in the ensovibep (vs. placebo) group at day 5 was 0.93 (95% CI, 0.67 to 1.30; P = 0.68; OR > 1 would favor ensovibep). The 90-day cumulative incidence of sustained recovery was 82% for ensovibep and 80% for placebo (subhazard ratio [sHR], 1.06 [CI, 0.88 to 1.28]; sHR > 1 would favor ensovibep). The primary composite safety outcome at day 90 occurred in 78 ensovibep participants (32%) and 70 placebo participants (29%) (HR, 1.07 [CI, 0.77 to 1.47]; HR < 1 would favor ensovibep).

Limitation: The trial was prematurely stopped because of futility, limiting power for the primary outcome.

Conclusion: Compared with placebo, ensovibep did not improve clinical outcomes for hospitalized participants with COVID-19 receiving standard care, including remdesivir; no safety concerns were identified.

Primary funding source: National Institutes of Health.

Publication types

  • Multicenter Study
  • Randomized Controlled Trial
  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • COVID-19 Drug Treatment*
  • Designed Ankyrin Repeat Proteins
  • Double-Blind Method
  • Humans
  • Recombinant Fusion Proteins
  • SARS-CoV-2
  • Treatment Outcome


  • Designed Ankyrin Repeat Proteins
  • Recombinant Fusion Proteins
  • ensovibep

Associated data

  • ClinicalTrials.gov/NCT04501978