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Table 1 Three representative COVID-19 scenarios for a symptomatic and a disease modification trial. No in-clinic visits are allowed during a 6-month interruption from March 19 to September 19, 2020. Bold text indicates significant distinctions between the two trials

From: Impact of potential modifications to Alzheimer’s disease clinical trials in response to disruption by COVID-19: a simulation study

  Symptomatic trial
Phase 2 symptomatic trial in mild-to-moderate AD
 • Daily oral medication
 • Planned outcomes at 12 months
 • N = 360 randomized to drug or placebo
Disease modification trial
Phase 2/3 disease modification trial for early AD
 • In-clinic monthly drug infusions
 • Planned outcomes at 18 months
 • N = 280 randomized to drug or placebo
Trial status on March 19, 2020 Fully enrolled Fully enrolled
97.5% completed 3 months 80% completed 3 months
67% completed 6 months 50% completed 6 months
45% completed 9 months 25% completed 12 months
22% completed 12 months 12% completed 18 months
Dropout 30% dropout rate evenly distributed across visits. No discontinuation due to COVID19 24% (66 subjects) discontinued before or on March 19 (partially due to COVID19). An additional non-COVID dropout rate of 25%. Final dropout rate: 42%a
Scenario 1 Trial stopped on March 19; no further visits or data collection
Scenario 2 Outcome assessments paused during COVID interruption, resumed after interruption.
• ~ 50%, who had completed 9 months, missed their 12-month outcome
• ~ 25% missed their 9-month outcome but could have 12-month assessments
• ~ 30% missed other outcomes
Medication continued during COVID interruption.
• ~ 50%, who had completed 12 months, missed their 18-month outcome
• ~ 25% missed their 12-month outcome but could have 18-month assessments
• ~ 50% missed other outcomes
Medication infusion paused during COVID interruption, resumed after interruption.
Scenario 3 No outcomes assessed during COVID interruption.
Medication continued during COVID, with extended medication provided beyond 12 months
Up to a 3-month extension of the final assessment window, to allow completion of 12 months outcomes after clinics reopened
Outcomes assessed remotely during COVID interruption; in-clinic assessment resumed after interruption.
Medication infusion paused during COVID interruption
No extension of the final assessment window
  1. aThe original expected dropout rate is 25%. In this scenario, 66 discontinued due to COVID-19, and because some would have been “potential completers,” the final dropout rate is approximately 42%. See trial construct 2 statistical methods