(En Español) As the Pfizer and Moderna vaccines against COVID-19 become available, it is critically important that Catholics and others have an accurate understanding of how these vaccines may be viewed from the perspective of Catholic moral teaching and tradition. The Vatican’s doctrinal office, the Congregation for the Doctrine of the Faith (CDF), has determined that it is “morally acceptable” for Catholics to take these vaccines against the COVID-19 Virus. Their determination is deeply rooted in the Catholic moral tradition. A brief review of their discernment in reaching this determination will assist people as they consider use of these vaccine and other vaccines. Vaccine development and production over the last several decades has often relied upon some cell lines that regrettably were originally developed from cells obtained from two fetuses that were aborted in the ‘70s and ‘80s. The Pfizer and Moderna vaccines are not dependent on these cell lines. They were developed using different technology relying on ribonucleic acid (RNA) from the virus itself. Even though the vaccines may have been tested using compromised cell lines, this does not establish a connection between the vaccine recipient and the abortion. Consequently, use of these vaccines is ethically sound. Other vaccines in development (including AstraZeneca and Johnson & Johnson) have been developed from compromised cell lines. The specific moral questions are whether a recipient of these COVID-19 vaccines developed from such cell lines is morally complicit in the original abortions, and whether use of the vaccine will lead others to have abortions. According to Catholic moral teaching and tradition, it is morally unacceptable for an individual or institution to contribute to and influence an immoral act committed by another in a way that shows they approve or intend the immoral act. It is also wrong for them to contribute components that are essential to the immoral act, even if they do not intend the act of the other, and to lead others by example to engage in an immoral act. Since it is impossible to influence an act that occurred in the past, a recipient of the COVID-19 vaccines developed from cell lines in question cannot influence or contribute to anything regarding the original abortions. Again, the mere fact that a vaccine may have been tested using these cell lines does not establish a connection between the vaccine recipient and the abortion. Furthermore, simply knowing the origin of the cell lines does not mean that one intends abortion. Thus, a recipient of the vaccine does not approve of or intend the original abortions, or materially contribute to them. Clearly, all that the recipient intends is the good preventing disease and saving lives. This includes protecting countless pregnant women from contracting COVID-19, who will be able to carry their unborn babies safely to term. The act of receiving the COVID-19 vaccines developed from the cell lines in question does not lead others to procure abortion. The action of the recipient is not the reason why someone has an abortion, nor is it an endorsement of abortion. Furthermore, vaccine researchers and others who develop cell lines from abortion-derived cells or use such cell lines in research do not lead persons to procure abortions. Researchers who develop or use these types of cell lines do so because they either see no connection of their work to abortion and/or because of the success of the cell line for research to develop effective and safe vaccines. On December 21, 2020, the Vatican’s doctrinal office, the Congregation for the Doctrine of the Faith (CDF), issued a statement noting it is “morally acceptable” for Catholics to take vaccines against COVID-19. Among other things, the CDF stated: "All vaccinations recognized as clinically safe and effective can be used in good conscience with the certain knowledge that the use of such vaccines does not constitute formal cooperation with the abortion from which the cells used in production of the vaccines derive” … “the morality of vaccination depends not only on the duty to protect one's own health, but also on the duty to pursue the common good." "In the absence of other means to stop or even prevent the epidemic, the common good may recommend vaccination, especially to protect the weakest and most exposed." Thus, the California Catholic Conference strongly encourages Catholics to receive a safe and effective COVID-19 vaccine for the sake of oneself, our loved ones, and the common good. If some of the faithful choose not to take the vaccine for reasons of conscience, the Vatican says those persons "must do their utmost to avoid … becoming vehicles for the transmission of the infectious agent.