Men Like Gods by H.G. Wells

The shadow of the great epidemic in Utopia fell upon our little band of Earthlings in the second day after their irruption. For more than twenty centuries the Utopians had had the completest freedom from infectious and contagious disease of all sorts. Not only had the graver epidemic fevers and all sorts of skin diseases gone out of the lives of animals and men, but all the minor infections of colds, coughs, influenzas and the like had also been mastered and ended. By isolation, by the control of carriers, and so forth, the fatal germs had been cornered and obliged to die out.

And there had followed a corresponding change in the Utopian physiology. Secretions and reactions that had given the body resisting power to infection had diminished; the energy that produced them had been withdrawn to other more serviceable applications. The Utopian physiology, relieved of these merely defensive necessities, had simplified itself and become more direct and efficient. This cleaning up of infections was such ancient history in Utopia that only those who specialized in the history of pathology understood anything of the miseries mankind had suffered under from this source, and even these specialists do not seem to have had any idea of how far the race had lost its former resistance to infection. The first person to think of this lost resisting power seems to have been Mr. Rupert Catskill. Mr. Barnstaple recalled that when they had met early on the first morning of their stay in the Conference Gardens, he had been hinting that Nature was in some unexplained way on the side of the Earthlings.