After doing a comparison of chart numbers in India...and applying the same formula to other areas...21 days after first shot sees little rise. 42 days after first shot (or 21 days after second shot) sees an almost doubling of cases in the charts...so a rapid rise about 3 weeks after the second shot.

worldmeters.info is the site I used.

I started with date vakzinations began in any given area, added 21 days to second set of doses to see the escalation.