[1] Since the cell strains in use originate from abortions,[2] there has been opposition to the practice and the resulting vaccines on religious and moral grounds.
[5] The Catholic Church has encouraged its members to use alternative vaccines, produced without human cell lines, if possible.
These are derived either from tumors, which have developed resistance to cellular senescence, or from stem cells originally taken from aborted fetuses.
[11] One of the first medical applications of cell lines derived from fetal tissues was their use in the production of the first polio vaccines.
Nevertheless, the Pontifical Academy for Life, concluded in 2005 that parents may allow their children to receive vaccines made from fetal tissue if no alternative exists and there is a grave health risk.
The moral duty to avoid such passive material cooperation is not obligatory if there is a grave danger," such as during the COVID-19 pandemic, and that "in such a case, all vaccinations recognized as clinically safe and effective can be used in good conscience" and "does not and should not in any way imply that there is a moral endorsement of the use of cell lines proceeding from aborted fetuses".