I would not beat yourself up on this. All vaccines or medications have some risk. The risk from this vaccine has been shown to be low, and as you say, the act

I would not beat yourself up on this. All vaccines or medications have some risk. The risk from this vaccine has been shown to be low, and as you say, the actual disease made him extremely ill already. It was perfectly reasonable advice to give. The symptoms sound more like long Covid though than vaccine related health issues (e.g. myocarditis).