I did not claim this is the case in general, but the phases the vaccine trials were conducted more parallel than usually would be the case. See Nature.com:
> The world was able to develop COVID-19 vaccines so quickly because of years of previous research on related viruses and faster ways to manufacture vaccines, enormous funding that allowed firms to run multiple trials in parallel, and regulators moving more quickly than normal.
No amount of parallelism is going to impact the fundamental time constraint of 1 human body. So it goes with pregnancy and so it must go for trusting long term impact. In an ideal world we'd know the second generational impact which would necessarily take 20-40 years. Referring to the awesome parallelism is a red herring to distract from the lack of long term controlled study.
> The world was able to develop COVID-19 vaccines so quickly because of years of previous research on related viruses and faster ways to manufacture vaccines, enormous funding that allowed firms to run multiple trials in parallel, and regulators moving more quickly than normal.
Source: https://www.nature.com/articles/d41586-020-03626-1