It would be a total disaster if the vaccine made things worse; it'd destroy trust in governments and vaccinations and our lock-downs would have been potentially worthless. It has to either work or we have to accept it'll take longer and deal accordingly. The risks of getting it wrong and implementing vaccination programs regardless are literally horrifying.
A death of a vaccine or a death of COVID-19 is still a death. We should act according to reduce the total number of deaths, taking into the probability we could be wrong (and if you say that probability can ever be zero, then I don’t believe you). A 0.01% chance we could kill more with the vaccine than without is not an excuse to not deploy it IF the alternative means more likely much higher deaths.
But luckily we don’t have a binary choice. A dead vaccine is usually much safer. We can start the vaccine to high risk groups early and watch carefully, expanding access as results come in. We’ve already started clinical human trials a month ago.
The 'calculated risk' you talk of is such a bad way to evaluate the risk of a vaccine making things worse that I shudder to think of the consequences should such an attitude be adopted. Please, just stop, and read about the consequences of getting a vaccine wrong.
Then you must be 'aware' that we can't simply calculate a probability of whether the vaccine will be worse or not. You either take a real gamble that it won't be, or you do the sane thing and actually observe long term effects in trials. There's no possible way you can assign probabilities like you can a coin flip - each vaccine and disease is far too unique and unpredictable.
Actually, you are taking a giant gamble with not vaccinating as well. You can, in fact, assign probabilities based on historical data. Epidemiologists do this all the time. To pretend probabilities don’t work in epidemiology means you don’t understand either probability or epidemiology.
There is no safe option. Every option will kill some people. Your goal is to minimize the expected number of deaths as best you can. That’s just the way it is. That may mean doing nothing OR it may mean finding a way to accelerate a vaccine program OR some combination of expanded early access with careful monitoring to stepped expansion of the treatment access.