One thing that is now beginning to be recognised by everyone, even by the medical corps, is that hygienic measures, for example, are effective only to the extent that one has confidence in them. Take the case of an epidemic. Many years ago we had a cholera epidemic here—it was bad—but the chief medical officer of the hospital was an energetic man: he decided to vaccinate everybody. When he discharged the vaccinated men, he would tell them, “Now you are vaccinated and nothing will happen to you, but if you were not vaccinated you would be sure to die!” He told them this with great authority. Generally such an epidemic lasts a long time and it is difficult to check it, but in some fifteen days, I think, this doctor succeeded in checking it; in any case, it was done miraculously fast. But he knew very well that the best effect of his vaccination was the confidence it gave to people.
Ref: Questions and Answers 1950 – 1951