My son (age 6) received his 4th Moderna COVID vaccine (2024-2025 booster- 3-11- .25 ML) at about 5 pm at a local pharmacy. He has not had reactions to the vaccine before. At 11 pm he woke us up and was covered in full body hives. We gave him benedryl and took him to the emergency room. The benedryl helped and he got no further treatment in the emergency room. He took zyrtec for a few days until the hives were gone. Follow up with pediatrician and allergist suggests this was an immune reactions. They do not recommend avoiding vaccines in the future, but perhaps switching brands.