That's not very true. Phase II trials are designed test safety, phasE III trials are designed to test efficacy. Statistics is advanced (and magic) enough that

That's not very true. Phase II trials are designed test safety, phasE III trials are designed to test efficacy. Statistics is advanced (and magic) enough that we're now reasonably sure that the vaccine has a 95% efficacy. That's not 'totally sure', we'll only be totally sure it works once everyone is vaccinated and the pandemic stops. But we _know_ it works, in the scientific-probabilistic meaning of knowledge.