Janet Kagan’s 1985 Uhura’s Song is a Star Trek: Original Series tie-in novel.
The starship Enterprise has been dispatched to Eeiauo, whose inhabitants have very reluctantly asked for help dealing with a virulent and quite deadly pandemic. This is not the first time ADF Syndrome has washed across this world — the last outbreak killed twenty thousand people — but it is the first outbreak that has forced the Eeiauoians to swallow their pride and ask for Federation aid.
A medical crisis would seem to be Doctor McCoy’s bailiwick. As it turns out, it is actually communications officer Lieutenant Uhura’s.
SPOILERS FOLLOW FOR THIRTY-FIVE-YEAR-OLD NOVEL