The COVID-19 pandemic

[tomh009]

Is there a reason to use a smaller trial though? I wouldn't think cost would be that big a factor, and recruiting participants should be easy right now.

One factor might be the trial location -- if AstraZeneca did their trial in the UK, and Pfizer/Moderna did it in the US, they would only have one fifth of the population to draw from.

That's pure speculation, though. Normally you would use a smaller trial size to speed up the process and reduce the costs, but, as you say, that shouldn't be the major factor here.