>It's worth pointing out that during a pandemic, while participating in a trial does carry a risk, so does not participating. A participant has some substantially greater probability* than the general population of avoiding an infection which apparently carries a risk of death or long term debilitating effects.
Participating also carries risks beyond simply that of the vaccine. Being exposed to any kind of healthcare setting is extremely dangerous right now. I'm taking part in the Moderna trial, and honestly I'm considering dropping out before the second injection. The risk of going into a clinic multiple times where I hear people coughing all over the place is starting to seem unacceptable to me given that I'm fairly certain I've been given the placebo.