This will be brief. I caught a two minute video put out by Dr. Bernstein, author of The Diabetes Solution, and long time advocate of low, low carb eating, on Facebook. He was talking about how the COVID-19 vaccine affected him. He said for almost two days afterward his blood sugar was exceptionally low, he had to drink 5 glucose drinks in a day. While he advocates getting the vaccine, he cautioned people to be alert and monitor your blood sugar.
Scrolling through the comments it appeared about half the people who have gotten the vaccine also experienced low blood sugar for a day or two after being vaccinated. A quarter seemed to go high and the remaining quarter seemed to have no affect. So, as all things diabetes, YDMV (Your diabetes may vary).
Just a word to the wise to monitor your blood sugar after the vaccine and be prepared for anything.