David Vetter and Ted DeVita were patients suffering from severe immunodeficiency. During their lives, they had to be protected from outside infections by, you guessed right, a bubble. In corona times this has come to mean something less tangible, but Paul S is singing here about the real thing.
The song was the opening song from the seminal album Graceland, an album of which I wrote earlier. What I found interesting though, is the B-side. It contains Hearts and bones, a song from the album of the same name. It was made a couple of years earlier, and features Paul Simon with almost the same style, but without the South African component.