"I have not, nor would I, call for Catholics to boycott the vaccine if it became available," he wrote.
Rather, he said, he and "other faith leaders" had asked the prime minister to seek out other vaccine candidates as well that would satisfy the ethical concerns of some faith communities.
The Oxford University/AstraZeneca vaccine candidate is one of the leading COVID-19 candidates in development, and one of several that uses the controversial HEK-293 cell line. Other candidates, such as those being developed by the company Sanofi Pasteur, do not use the HEK-293 cell lines.
Pope Francis last week called on countries to help ensure that new coronavirus vaccines are "universal and for all" rather than "the property of this nation or another."
The Vatican document Donum Vitae said regarding the use of fetal tissue of aborted babies in research, that "The corpses of human embryos and fetuses, whether they have been deliberately aborted or not, must be respected just as the remains of other human beings," and that "the moral requirements must be safeguarded that there be no complicity in deliberate abortion and that the risk of scandal be avoided"
The 2008 Vatican document Dignitas Personae said that researchers have "a duty to refuse to use such 'biological material' even when there is no close connection between the researcher and the actions of those who performed the artificial fertilization or the abortion. Parents, however, could justify the use of vaccines developed from aborted fetal cell lines for "grave reasons."
In 2017, the Pontifical Academy for Life addressed the topic again, saying that "the cell lines currently used" in common vaccines "are very distant from the original abortions and no longer imply that bond of moral cooperation indispensable for an ethically negative evaluation of their use."
Furthermore, the statement noted that "the moral obligation to guarantee the vaccination coverage necessary for the safety of others is no less urgent, especially the safety more vulnerable subjects such as pregnant women and those affected by immunodeficiency who cannot be vaccinated against these diseases."