In 1976 we rushed a vaccine without adequate safety tests (formal clinical trials) and more people were hurt by the unsafe vaccine than would have been sick without the vaccine.
You know, what would be cool is if we'd managed to make some progress on immunology and pharmacology in the past 40+ years, such that we could avoid mistakes like that.
It'd be cool if you could always deliver a bug free software program without thorough testing, on-time, on-scope, 100% of the time too... that'd be really nice. It's just not likely.
In software there's things your overlook, etc... I'm guessing biological 'hacking' is the same, I'd imagine making a vaccine is similar in a lot of ways to coding - lots of trial/error, except errors = dead people.
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.