Sounds like ulcer or defect in digestive tract.
He was losing weight for 4 months. The vax Jan was more recent. Common sense tells you this kid was already sick and should have skipped the jab. You don’t need to buy home insurance if the house is destroyed already. Vax is not a cure or prevention. It is only insurance to avoid serious attack of covid. Why would a kid with severe digestive issues be subjected to stress of the jabs?