Good question. Not sure about the efficacy of delaying the second shot but it appears to be 90% effective with the first. The economist side of me says we should have given only first shots to more people because getting an additional 7% effectiveness for each second shot is nowhere near the bang for the buck to get more people the 90% effectiveness of a first shot. That was what drove the decision in the UK and it appears to have been the case.
Sounds like you've heard the same as me that more people are having issues with the second shot. My 88 year old Mom with COPD and some heart issues had her second shot with no issues other than a sore arm. I am still in a holding pattern on the vaccine until some more time has elapsed to see if there are issues. I just saw that Denmark (I think) temporarily halted one of the vaccines due to some clotting issues. This has to be the biggest drug trial in history and only time will tell. Either way, Operation Warpspeed was a miracle of science and occurred mostly because the bureaucracy got out of the way. Only to reassert itself with the distribution.
Saw some idiot investigative reporter complaining about long lines at a FEMA distribution site in Florida and tried to blame DeSantis. The media is truly stupid and the enemy of the people. FEMA.....begins with Federal......sigh.......