A senior Catholic archbishop has warned he is “deeply troubled” by Australia's vaccine deal with AstraZeneca, saying the potential vaccine uses a fetal cell line that creates an “ethical quandary” for Christians, according to AFP.

Sydney Archbishop Anthony Fisher penned a letter — also signed by Anglican and Greek Orthodox religious leaders — to Prime Minister Scott Morrison outlining concerns of some Christians over the vaccine's apparent use of a cell line derived from an elective abortion performed decades ago.

The letter, seen by AFP, calls on Morrison to ensure that if the vaccine being developed by Oxford University researchers is rolled out in Australia it is not made mandatory.

It also urges him to pursue other “ethical” vaccine candidates to ensure religious objectors have a choice.