I am also dealing with this post- Moderna Covid booster. Hives began 10 days after the booster. Dr. prescribed 12 days of prednisone, which got rid of the hives but I now have dermatographia. Photos attached of initial hives and dermatographia. Just completed the prednisone and dermatogrphia seems to be improving slowly. I am now taking one Zytec per day. Fingers crossed the hives don't return.