The vaccine for Measles, Mumps and Rubella was created using cells from aborted fetuses in the 1960s. While subsequent vaccines have not been created through the direct death of an unborn baby, many of them are created using the cell lines from the same aborted fetuses from which the MMR vaccine originated. So, the question arises - if I have my children vaccinated with vaccines developed from aborted fetuses, am I not cooperating in the death of these unborn victims? Yet, to leave my children unprotected from serious diseases cannot be morally acceptible, can it?
It is exactly such moral dilemmas for which principles such the principle of legitimate cooperation with evil and the principle of double effect exist.
Some well-meaning Catholics reject these principles because the principles seem to lean too far toward our culture's philosophy of moral relativism. They forget that applying moral principles in a fallen world can be messy and sometimes confusing. True, these principles are often misused by those who want to appear to remain within the norms of Catholic morality while living as if the moral law does not exist. However, when they are properly used, these principles are valuable tools for those who truly seek what is objectively right.
The first principle of morality is to always choose good and avoid evil. Your choice to vaccinate your children against potentially dangerous illnesses is a fundamentally good choice. You are exercising your parental responsibility to protect your children.
In this case, your intentions mirror the moral object. You are choosing to protect your children against diseases. The murder of innocent life is definitely evil, but it is not an evil that you choose or that you agree with. You would avoid it if you could. It is only tolerated as unavoidably intertwined with the good you are choosing to do.
