Some vaccines—rubella, HepA, RAB-HDC, VAR, ZOS, and one form of IPV (the Poliovax contained in Pentacel)—are grown in cultured human embryo fibroblast cell lines (WI-38 or MRC-5) because these are the only cells that replicate the viruses in high enough titer for mass production (the rubella vaccine strain itself was originally isolated from an aborted fetus with intrauterine infection). Each of these cell lines was first obtained from an aborted fetus in the early 1960s. These very same embryonic cells have been passaged in tissue culture in the laboratory since then. Whereas no new fetal material has ever been involved, this situation does represent a moral dilemma for some people.
In helping patients work through this, it may be worth emphasizing that the original abortions were not done with the intent to produce vaccines (they were done for therapeutic reasons, and the intent of culturing the cells was to understand immortalization and oncogenesis), that they occurred in the distant past, that the modern day vaccine producers never intended for fetuses to be aborted, and that the moral imperative to save lives through vaccination might outweigh their objection to a singular, distant moral transgression. Many religious organizations, including the United States Conference of Catholic Bishops, have used these arguments to support vaccination, despite their opposition to abortion.
—Marshall, Gary S. “Addressing Concerns About Vaccines.” The Vaccine Handbook: A Practical Guide for Clinicians. 3rd ed. New York: Professional Communications, Inc., 2010. 217-218. Print.