COVID-19 Vaccines and Fetal Tissue: The Science and Controversy Explained

pope francis  covid-19 vaccine fetal cells abortion
The COVID-19 vaccines used fetal cells from aborted human embryos in their development, creating a moral challenge for Catholic leaders. Pope Francis in the Basilica of Santa Maria in Aracoeli, on October 20, 2020 in Rome. ANDREAS SOLARO/AFP via Getty Images

In 1972, Alex van der Eb, a molecular biologist, took cells from an aborted human embryo and cultured them in his lab in Leiden University in the Netherlands. The cells have since become "immortal," meaning the descendants of the original cells have played a role in the research of numerous vaccines, including rubella, adenovirus, polio, rabies, chickenpox, Ebola and, most recently, several of the most widely used coronavirus vaccines.

That puts the Roman Catholic Church, which opposes abortion and any use of cells obtained from human embryos, in a tough spot. Since 2005, the Vatican has made an exception for vaccines for diseases that pose a "grave danger" and for which there are no "morally acceptable" alternatives, and it confirmed this stance for the coronaviruses in December: "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." Pope Francis took this advice to heart by taking Pfizer's COVID-19 vaccine.

However, in early March, Catholic Bishops in the U.S. muddied the waters by calling out the Johnson & Johnson vaccine as having "additional moral concerns." At issue is the precise role fetal-cell lines played in the development of the vaccine. While Moderna and Pfizer used them in testing only, J&J also used them in the production of its vaccine. "If one has the ability to choose a vaccine," the bishops said, "Pfizer or Moderna's vaccines should be chosen over Johnson & Johnson's."

The Bishops' moral concern arises from the relative proximity of the J&J vaccine to the "evil" of abortion.

Fetal-cell lines played a vital role in the development of all three vaccines. Moderna and Pfizer used Van der Eb's original cell line, called HEK 293, in the testing of their coronavirus vaccines—that is, scientists first developed the vaccines using their mRNA technologies and subsequently tested them on lab-cultured HEK 293 cells, ancestors of the original cells that Van der Eb took from an embryo almost 50 years ago. Johnson & Johnson used a different fetal-cell line, called PER.C6, that was cultured in Van der Eb's lab in 1995.

While Moderna and Pfizer used fetal cells for testing their vaccine after it was already produced, J&J used fetal cells as tiny "factories" that produced the active ingredient in its vaccine. It was inside PER.C6 cells where a gene for the coronavirus' spike protein was attached to a modified adenovirus. (The vaccine works when the adenovirus infects human cells and the added gene instructs the cells to manufacture the spike protein, which elicits an immune response.)

Doses of Johnson & Johnson COVID vaccine
Doses of the Johnson & Johnson COVID vaccine are packaged in a box at the McKesson facility on March 1, 2021 in Shepherdsville, Kentucky. Timothy D. Easley-Pool/Getty Images

The Moderna and Pfizer vaccines are morally acceptable, according to the Archdiocese of New Orleans, because their scientists did not use the cells in the "manufacturing process," which means that "the connection to abortion is extremely remote." The J&J vaccine, by contrast, "is morally compromised as it uses the abortion-derived cell line in development and production of the vaccine as well as the testing."

Public health officials worry that this judgment will give anti-vaccination groups ammunition to sow doubt about vaccines in general, and coronavirus vaccines in particular. "Diehard anti-vaxxers use it," Arthur Caplan, a bioethicist at New York University, told Newsweek. "They'll say, 'Catholics won't take it because there's something wrong with it.' They don't care about the details; they're just going to stir the pot. And it's a pot they need to stir because they've been losing the safety argument in the past few years."

Pockets of vaccine hesitancy in the U.S. and elsewhere could delay herd immunity to the coronavirus, costing lives. With 50 million Catholics in the U.S. and 1.3 billion worldwide, seeds of doubt have plenty of room to grow. "It's a dangerous path," says Caplan.