In phase 3 trial, there should be a regular follow up at set intervals, let’s say every 6 weeks, then every 9 weeks, etc. In the wild in the US healthcare realities if you receive a vaccine and then either have a breakthrough infection or any not immediate side effect, it’s not clear when this information will get back to CDC, so they can properly analyze it. Israel had much smaller data set(small population), yet they noticed myocarditis sooner.