What does "can" get covid mean? People either get it, whatever "it" is, or they don't. If they don't get it, then why are they in the 48%? And what if they get "it" a month later? What about those with some sort of natural immunity? Are they included in the 52%? How many people are in one of these trials anyway? Are they double-blind? Can we be sure it's 52% and not 51% or 53%?
Did you ever take a course in statistics?
ML/NJ
It is pretty clear to me. Early immunity sets in as antibodies, for which few can be infected while those are in one's body. Then those fade away, leaving people vulnerable, at its worst, 52% have enough residual immunity to stop a COVID-19 infection. Then, with the second dose, it drives the T-cells to finish creating the long term immunity that leaves nearly everyone unable to get COVID-19.
We need to assume that to get those percentages, efforts were made to infect people or to check the adequacy of their immunity levels throughout the time reviewed.
Maybe your problem is that the human immunological response is not clicking in your mind.