I agree with your response, it's a logical concern. However we're going to try dozens of vaccines on probably 500k-1m people in total globally before deploying

I agree with your response, it's a logical concern. However we're going to try dozens of vaccines on probably 500k-1m people in total globally before deploying them in an increasingly broad way. The next stage of the Pfizer-BioNTech trial is going to be 30,000 in July/August.