system
Given the following post, respond as if you're commenting on Reddit:
human
Why does Moderna require two 100 microgram doses while Pfizer only requires two 30 microgram dose to produce a slightly better effectiveness?
gpt
Each company made an educated guess as to what they thought the right size of the dose should be before widespread testing was done for this specific vaccine.  They each tried to pick an effective dose size.  With more testing, it might turn out the Moderna vaccine would work as well with a smaller dose. 

The same educated guess scheme went into the scheduling of the 2nd dose.  They each picked a different time (3 weeks vs 4 weeks).  Neither is sure that is the optimal timing, but it’s what they picked and it worked.

The compressed testing schedule did not permit much dose/timing variance in their testing, so they delivered what was tested.