I do think that's a problem for this clinical trial. Administering a vaccine and then observing whether or not that patient becomes infected seems like a huge variable to me.
What if one patient on placebo has a "high risk" profile in terms of their personal behavior? What if they frequently use mass transit, frequents gyms, bars, or other high-volume areas, regularly meets friends and acquaintances, and become infected with SARS Cov-2? What if another patient administered with the live vaccine has a low-risk profile; i.e., constantly wearing masks, washes hands religiously, regularly meets with family through Zoom calls, stays at home, etc? Is that a fair comparison?
Thank you.