I think the chances that it is unsafe are zero. Someone in the UK would have noticed by now, they vaccinated quite a lot of people.
The interesting question that needs to be answered is: to what degree does it work, and for which groups? Of course it would be possible to just widely distribute the vaccine (since I consider it safe) and run the study to answer that question in parallel. In the worst case, you widely distributed an expensive placebo. Don't know if that is a good idea overall however.
In my mind the worst case is we hold off on distributing it for a couple of months. And later find out that it was far more effective at preventing death/hospitalization than symptoms. So we end up 1,000 more dead than we would have if we vaccinated with the AZ vaccine.
I guess the problem with rolling out ineffective vaccines is if you waited a little you might have got a better one. Guess it depends a bit on how long it'll take to crank up the others.
