An interesting point on medical ethics, it's actually really unethical to give people huge rewards for participating in drug trials. If you promise someone $10,000 to try a vaccine then that's basically a coercive amount of money - for people out of a job it's an offer they can't refuse.

A smallish reward like $50-$100 is large enough to compensate people for their help but small enough to not get people who are desperate for money.