You cannot see these kinds of very rare side effects in typical phase III trials. Those trials are already pretty large for vaccines, but even then they're simp

You cannot see these kinds of very rare side effects in typical phase III trials. Those trials are already pretty large for vaccines, but even then they're simply not powerful enough to detect very rare events. Nothing would have changed here with the normal vaccination approval process, those side effects would not have been detected there either. That's why side effects are monitored after approval of the vaccines as well, because then you have the large numbers you need to detect very rare events.