There was a very rare side effect in the Astra Zeneca vaccine that was discovered quite quickly. Not in the original trials as they are simply not powerful enou

There was a very rare side effect in the Astra Zeneca vaccine that was discovered quite quickly. Not in the original trials as they are simply not powerful enough to detect side effects that rare, but in later observations. We also pretty quickly figured out that the risk is age-related, and many regulating authorities reacted based on that and adjusted the recommendations. To me this is pretty good evidence that the existing mechanisms for detecting rare side effects work in general. One can argue about the details in this case on how exactly the authorities responded, and I think also reasonably disagree on how to weigh the risk/benefit in this particular case for specific age groups. But those are much more difficult questions based on inherently fuzzy data due to the low frequency of this serious side effect. But the detection itself worked well, and also produced very quick reactions.