The claim is(I can't find the article, but I've read several), that the vaccine(specifically the mRNA vaccines and the vector vaccines) become your primary immune response and suppress or even inhibit your own natural immune response. Those vaccines were engineered to specifically target a certain spike protein in the virus, whereas your natural immune system is more broad based. When a new variant comes along, your protection will be reduced compared to not having gotten the vaccine after already having been previously infected.