I have LBBB along with other heart rhythm issues, also high BNP. I was diagnosed with cardiac sarcoidosis as a cause and am also being treated for that problem. I had a CRT-D installed and am doing much better. I too was concerned about the vaccine since shortly before my diagnosis I to received the latest dose of the COVID vaccine, however, in talking to all my doctors I have come to the conclusion it is more coincidence vs causation. Good Luck. Hopefully you feel better as I have after ICD/CRT.