A separate thread started on this topic. I added these comments there, and thought they could be helpful here, too:
Another way it could help to think about this is to know: It is also possible to make human cell lines from adult stem cells or from surgically resected human cancer tissue. (But note, that it is not possible to take just any type of cell from a human body and make a cell line. The types of cells that can be used to generate cell lines, cancer or stem cells, have particular properties that enable them to continue growing and dividing)
When scientists take cells from an adult skin, blood or cancer and turn them into a cell line, we do not say that those cells are still the person that they came from. Those cells do not have a soul or personhood. They are just cells that have been transformed in such a way that they continue to divide and can be continually cultured under special conditions in the laboratory. We have no ethical challenges using them.
Likewise with the fetal-derived cell lines. It is a tragedy that the abortion happened. However, that baby, that person, died decades ago. I believe that their soul is in heaven with Jesus now. The cells derived from the deceased baby were taken from one of the baby’s tissues after the baby died. Now those cells have been cultured under special conditions in the laboratory for decades. The ethical issue that people need to grapple with is the abortion, not the propagation of individual cells derived from individual tissues (like the human embryonic kidney, HEK cell line used in research laboratories). In my opinion, getting vaccinated does not make someone complicit in an elective abortion that happened decades ago.