https://en.wikipedia.org/wiki/Use_of_fetal_tissue_in_vaccine_development
Most vaccines currently available were developed using cell strains cultured from two fetuses aborted for other purposes in the 1960s.[3] This has led some to oppose vaccination on religious or moral grounds.[1][2]
However, vaccine experts and manufacturers state that vaccines do not
contain any of the original fetal tissue or cells, that the abortions
occurred decades ago and replenishment with new tissue has not occurred.
Also, producing a safe vaccine for many diseases requires the use of
these cell strains.[2] The Catholic Church, which opposes abortion, has stated that vaccination should not be refused on moral grounds because the public health benefits of vaccination outweigh the historical use of aborted fetal tissue to develop some vaccines.[1][2]