I read the article you refer to, @sybonbon , and I think you have misunderstood. The vaccines boost our immunity for the disease they are designed for; but then, over time, that immunity drops down. It’s still way higher than it would have been without the vaccine, but is decreasing from that initial high amount.
But the decrease does not reduce your immune “system”, only the immunity for that specific virus. So, after time has passed, a booster shot for the virus maintains protection against that virus.