Immunology.

The only way this virus could break from the norms of immunity, is if it directly affected our memory T-cells and B-cells.

Critically, it would also have to impair those cells without impairing their ability to clear the virus the first time... or else the patient would be dead after the first round.

This is not happening with this virus.

If someone successfully fought off a first infection, an actively infectious person could litterally cough into their mouths...  And still, the person with immunity would not show symptoms later on.