Impact of allocation concealment and blinding in trials addressing treatments for COVID-19: A methods study

Objective: Assess the impact of allocation concealment and blinding on the results of COVID-19 trials. Data sources: World Health Organization (WHO) COVID-19 database (up to February 2022) Methods: We included randomized trials that compared drug therapeutics with placebo or standard care in patients with COVID-19. We performed random-effects meta-regressions comparing the results of trials with and without allocation concealment and blinding of healthcare providers and patients. Results: We identified 488 trials. We found that, compared to trials with allocation concealment, trials without allocation concealment may estimate treatments to be more beneficial for mortality, mechanical ventilation, hospital admission, duration of hospitalization, and duration of mechanical ventilation, but results were imprecise. We did not find compelling evidence that, compared to trials with blinding, trials without blinding produce consistently different results for mortality, mechanical ventilation, and duration of hospitalization. We found that trials without blinding may estimate treatments to be more beneficial for hospitalizations and duration of mechanical ventilation. Conclusion: We did not find compelling evidence that COVID-19 trials in which healthcare providers and patients are blinded produce different results from trials without blinding but trials without allocation concealment estimate treatments to be more beneficial compared to trials with allocation concealment. What’s new? Additional information: For decades, allocation concealment (the concealment of the randomization sequence from personnel enrolling participants) and blinding (the concealment of the arm to which participants have been randomized from one or more individuals involved in a trial) have been important considerations in the assessment of risk of bias of trials. Previous studies have produced conflicting results with regards to the associations of blinding and allocation concealment and none have investigated the associations of allocation concealment and blinding in the context of COVID-19. Implications: Our study suggests that lack of blinding may not always bias results but that evidence users should remain skeptical of trials without allocation concealment.