In general
Phase 1 : 10s -occasionally low 100s of people
Phase 2 : 100s people
Phase 3 : sometimes up to 10 000s people ( in large, multi-centre, often international trials)
Covid vaccine double dosed (U.K. only):
39 500 000 people
This has been authorised by the UK regulator, following completion of extensive trials. The threshold for safety and efficacy being set extremely high.
The only reason it is not formally licensed is because we are in the middle of a pandemic, so there are differences around liabilities the manufacturers and sponsors have to take.
The level of scientific rigour and the medical standards this drug is held to are no different than any other drug.
Anyone who tries to blithely claim this drug is still in a clinical trial is being deliberately misleading, misrepresenting information for the purposes of scaring others, and an out-and-out anti-vaxxer.