To understand you right:
He did get the usual vaccines according to established schedule, like smallpox, mumps, scarlet fever and all other stuff they give to babies and kids today, and on top of that he also got a covid vaccine? If so, which one, i.e. which brand?
If he got the regular ones, somewhere around age 6 and certainly before going to school as it is a prerequisite, or at least it was 10 years ago, there is going be an additional, IRC, the TBC one. The son of my ex-ex had rather a reaction to it soon after he got it, with fever and affecting his immune system.
In that regard, if you aren't going to manage to avoid that 'obligation', maybe
@Regulattor might have some useful info or advice to share.