Of great concern to some parents has been the question of vaccines derived from aborted fetal tissue. This has been an issue for some time, that came to the fore especially when the chicken pox vaccine became available and then required in many states.

Here’s a recent Vatican statement on the vaccines and moral culpability:

From the point of view of  prevention of viral diseases  such as German measles, mumps, measles, chicken pox and hepatitis A, it is clear that the making of effective vaccines against diseases such as these,             as well as their use in the fight against these infections, up to the point of eradication, by means of an obligatory vaccination of all the population at risk, undoubtedly represents a "milestone" in the secular fight of man against infective and contagious diseases.

However, as the same  vaccines are prepared from  viruses taken from the tissues of foetuses that had been infected and voluntarily aborted, and the viruses were subsequently attenuated and cultivated from human cell lines which come likewise from procured abortions, they do not cease to pose ethical problems.   The need to articulate a  moral reflection on the matter in question arises mainly from the connection which exists between the vaccines mentioned above and the procured abortions from which biological material necessary for their preparation was obtained.

If someone rejects every form of voluntary abortion of human foetuses, would such a person not contradict himself/herself by allowing the use of these vaccines of live attenuated viruses on their children? Would it not be a matter of true (and illicit) cooperation in evil, even though this evil was carried out forty years ago?

Before proceeding to consider this specific case, we need to recall briefly the principles assumed in classical moral doctrine with regard to the problem of cooperation in evil ⁹,  a problem which arises every time that a moral agent perceives the existence of a link between his own acts and a morally evil action carried out by others.