[peter422]

The past vaccine timeline was driven mostly by monetary concerns and not safety ones. Companies did not want to risk spending tons of money on large trials until they were sure all the smaller ones were bulletproof.

Once you get to the point of doing the large phase 3 trial the timeline for these vaccines was much less compressed. Also much easier to test a vaccine when the virus is spreading all over the place quickly.

Also there just aren’t historical examples of vaccines having “hidden” long term effects. All side effects that happen after 6 weeks also happen much more frequently before 6 weeks.