Hospital Ship 4-2 was a large Dinaali medical vessel hovering over a polluted city, where a computer called the Allocator decided each patient's treatment according to social worth.
The ship is the setting of the Voyager episode Critical Care. The trader Gar steals the Doctor's mobile emitter and sells him to the hospital's administrator, Chellick, who puts him to work on Level Red, a crowded ward for ordinary people where medicine is strictly limited.
The Doctor learns that each patient has a treatment coefficient based on their usefulness to society. On Level Blue the favoured receive a drug, cytoglobin, as a routine tonic, while a boy named Tebbis is left to die for want of it on the floor below.
After failing to change the system by smuggling medicine, the Doctor injects Chellick with the virus and alters his records, so that the administrator can be treated only by releasing drugs to Level Red.