The Goldberg, et al. "hybrid immunity" study found that rates of infection for recovered + vaccinated were a hair lower than for recovered alone, at 4-8 months (https://www.medrxiv.org/content/10.1101/2021.12.04.21267114v1). That would suggest the reinfection of your contact's son is unusual.

However, that was before Omicron. It could be that a lot of the "reinfections" we are hearing about w/ Omicron are cases just like that - infection + vaccine + Omicron. Either having high residual antibodies is not good when it comes to Omicron, or the vaccine causes the immune system to deprioritize the full spectrum immune response (against all the epitopes associated with the virus) in favor of the spike. In either case, the recovered+vaccinated looked like they weren't being disfavored before but now that the spike is more mutated, the damage becomes clear.

And then there's general immune suppression, anecdotally this is well supported. Again, this was hidden before by the "anti-spike immunity" but the spike is too different now.

Both possibilities discussed at https://unglossed.substack.com/p/neg