The Health Risk

13. As previously stated, one of the fundamental ethical questions that should be examined when judging the legitimacy of xenotransplantation is that of the health risk involved in such procedures. This risk is dependent on various factors which cannot always be predicted or assessed. Before going on, therefore, it may be useful to recall some general aspects of the ethics of risk.

Risk - understood as an unwanted or damaging future event, the actual occurrence of which is not certain but possible(⁶⁵) - is defined by means of two characteristics:  the level of probability and the extent of damage. The probability of the occurrence of a certain damaging event in particular circumstances can be expressed as a risk percentage or as a statistical frequency. Furthermore, the presence or absence of certain chance factors of risk can sometimes alter the probability that a certain event will take place. The extent of the damage, in contrast, is measured by the effects that the event produces. Naturally, a very probable risk is easily tolerated if the extent of damage associated with it is very small; on the contrary, a risk that causes a high level of damage, however improbable, gives rise to much greater concern and require greater caution.

It is important to distinguish between a probable event (albeit with varying degrees of probability) and an event that is only hypothetical; this latter is an event which is not theoretically impossible but which is so improbable as to require no change in behaviour or choices.

Together, these two criteria - probability and extent of damage - define the acceptability of the risk, as reflected by the risk/benefit ratio. Only when a risk can be concretely assessed it is possible to apply criteria for evaluating its acceptability.

Lastly, it is necessary to distinguish acceptability from what we can define as the acceptance of the risk, as defined by the reaction of the individual or of the general public to the existence of the risk. This is a response that has a significant subjective component, one which is not always completely thought out and which is influenced by culture, by the information available and how it is understood, by the way in which the information itself is communicated, and by common sensibilities.(⁶⁶)

In the absence of data that allow a reliable assessment of such a risk, greater caution should be used; this does not necessarily mean, however, that a total "block" should be put on all experimentation. Indeed, to move from ignorance to knowledge, from the unknown to the known requires the exploration of new approaches which in all likelihood, especially during initial experimental stages, will not be without risks, at least potentially. In this situation, therefore, the imperative ethical requirement is to proceed by "small steps" in the acquisition of new knowledge, making use in experiments of the least possible number of subjects, with careful and constant monitoring and a readiness at every moment to revise the design of the experiment on the basis of new data emerging.

It is important to consider the distinction between risk assessment and risk management. To achieve an ethical assessment, both elements must be carefully examined.