The use of Covid-19 vaccines developed using cell lines derived from aborted foetuses is "morally acceptable", the Catholic Church announced on Monday.
In the absence of any alternative, such vaccines "can be used in good conscience", the Vatican said.
It added that this would "not constitute formal co-operation" with the terminations that took place.
Several vaccine candidates were developed using cells derived from foetuses aborted decades ago.
However, no foetal cells are present in any of the vaccines.
"All vaccinations recognised 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 co-operation with the abortion from which the cells used in production of the vaccines derive," the Vatican's Congregation for the Doctrine of the Faith announced in a statement on Monday.
The text, which was approved by Pope Francis, also said there was "a moral imperative" to ensure that poorer countries received access to effective vaccines.
The issue of whether to accept a coronavirus vaccine has divided some members of the clergy, with the US Conference of Catholic Bishops arguing in favour last week.
"Given the urgency of this crisis, the lack of available alternative vaccines, and the fact that the connection between an abortion that occurred decades ago and receiving a vaccine produced today is remote, inoculation with the new Covid-19 vaccines in these circumstances can be morally justified," a document published by two of the group's members said.
It said the inoculations produced by Pfizer/BioNTech and Moderna, which both used a cell line derived from an aborted foetus to test their vaccines, were preferable to the Oxford/AstraZeneca vaccine, which used such cells in the design, development, production and testing stages.
Where no choice was available, however, "it would be permissible to accept the AstraZeneca vaccine", the document said.
Several of the countries with the highest numbers of coronavirus cases have significant Catholic populations, including Brazil, Mexico, Italy and Spain.
The news of the Vatican's decision on the issue came as AFP news agency reported that two cardinals close to Pope Francis had tested positive for coronavirus.