The lyric is a much more natural fit in "Levitate". It does not seem to fit well with the rather pessimistic point of view of the rest of "Miracle Drug".
Pessimistic point of view? For me it's an extremely uplifting song. The message behind it is that with love and science, "miracles" can happen and people are saved through medical advances. I think it's a very positive message, that humanity has a kind of control over its own destiny to an extent. I seem to remember Bono saying during the Vertigo tour, that the song was an expression of thanks towards doctors and other medical staff (presumably in regards to his father).
I read something different from Bono saying this song is about a boy whose mother he met, and that boy has a very rare disease and noone has an idea to help him. I don't know what it is exactly but part of it is, that the boy is kind of locked up in his own head, can't speak and express, but his mind is fully present. So both mum and boy hoping for a miracle drug. But already, with a lot love, they found a way to communicate tho she still doesn't know what he really sees, hears, feels, thinks and realizes "I want a trip inside your head, spent the day there" and since sure she still sees him as her little baby boy, the newborn baby line makes totally sense to me. Since love can't do it all, they both hope for more "I've had enough of romantic love, I'm not giving up on a miracle drug" since we already know what science is able to do today.
And yes, it's a very positive song.