Now it will be clear why in our period the protection of vaccination appeared. We also understand why, among the best minds of our period, there exists a kind of aversion to vaccination. This aversion corresponds to something within, and is the external expression of an inner reality. So if on the one hand we destroy the physical expression of a previous fault, we should, on the other hand, undertake the duty of transforming the materialistic character of such a person by means of a corresponding spiritual education. This would constitute the indispensable counterpart without which we are performing only half our task.
We are merely accomplishing something to which the person in question will himself have to produce a counterpart in a later incarnation. If we destroy the susceptibility to smallpox, we are concentrating only on the external side of karmic activity. If on the one side we go in for hygiene, it is necessary that on the other we should feel it our duty to contribute to the person whose organism has been so transformed, something also for the good of his soul. Vaccination will not be harmful if, subsequent to vaccination, the person receives a spiritual education. If we concentrate upon one side only and lay no emphasis upon the other, we weigh down the balance unevenly.
Source: Rudolf Steiner – GA 120 – Manifestations of Karma: Lecture: Karma of the Higher Beings – Hamburg, May 25, 1910