Fetal cell lines in vaccines are laboratory cell cultures descended from tissue taken from three elective abortions performed decades ago — two in the 1960s and one in 1985 — that are used to grow the viruses inside a handful of vaccines. No new fetal tissue has been collected for this purpose since those original derivations. The cells were frozen into master banks early on, and manufacturers thaw vials from those banks as needed, so the same original cultures have supplied global vaccine production for more than fifty years.
Only a few vaccines on the U.S. schedule are actually manufactured this way, and the mRNA COVID-19 vaccines most people ask about are not among them.
Which Vaccines Are Made With Fetal Cell Lines
The vaccines produced directly in human fetal cell lines are:
- The rubella component of MMR (grown in WI-38). The measles and mumps components of MMR are grown in chick embryo cells, not human cells.
- Varicella (chickenpox).
- Hepatitis A. All U.S.-licensed hepatitis A vaccines use MRC-5.
- One version of the rabies vaccine, sold as Imovax.
The Johnson & Johnson (Janssen) COVID-19 vaccine was manufactured using the PER.C6 line, but it is no longer available in the United States.
Testing Is Not the Same as Manufacturing
The Pfizer and Moderna mRNA COVID-19 vaccines were not manufactured in fetal cell lines. Researchers did use HEK-293T cells during early laboratory testing to confirm that the vaccine’s mRNA could produce the spike protein, but those cells were never part of the production process and no residual material from them ends up in a dose. This distinction matters generally: when a cell line is the growth medium during manufacturing, trace host-cell material has to be purified out of the final product; when a cell line is only used for confirmatory testing during development, it never enters the production pipeline.
Where the Cell Lines Came From
Four cell lines account for essentially all fetal-cell-derived vaccine production.
WI-38 was developed by Leonard Hayflick at the Wistar Institute in 1962, from the lung tissue of a female fetus at roughly three months of gestation following an elective abortion in Sweden.1ATCC. WI-38 (CCL-75) MRC-5 was derived by J.P. Jacobs in September 1966 from the lung tissue of a 14-week-old male fetus in the United Kingdom. Both are diploid strains with a built-in replication limit of about 50 divisions, which is why manufacturers preserved early-passage vials in liquid nitrogen master banks and draw from them for each new production run.
HEK-293 was created in 1973 by Frank Graham, who transformed human embryonic kidney cells using fragments of adenovirus DNA, giving the cells the ability to replicate indefinitely.2Government of Canada. Recognizing the Scientific Impact of Dr. Frank Grahams HEK 293 Cell Line PER.C6 was derived from the retinal cells of an 18-week-old fetus from a 1985 pregnancy termination and was formally established as a production line in 1998.3National Center for Biotechnology Information. HEK293 Cell Line as a Platform to Produce Recombinant Proteins and Viral Vectors Both are immortalized through genetic modification.
Human cell lines are used for certain vaccines because some viruses behave more naturally in human cells than in animal tissue. Influenza viruses grown in chicken eggs, for instance, can pick up mutations that make the vaccine strain less similar to the strain actually circulating, reducing protection.4Centers for Disease Control and Prevention. Cell-Based Flu Vaccines
What Ends Up in the Final Vaccine
After the virus has replicated in the cell culture, the manufacturing process shifts to purification. Centrifugation and chromatography strip away the growth medium and cellular debris, leaving the viral antigen along with stabilizers and preservatives.
Trace amounts of residual host-cell DNA can persist. The FDA and the World Health Organization cap this residual DNA at 10 nanograms per dose for vaccines produced in continuous cell lines, and any remaining DNA fragments must be smaller than 200 base pairs.5Food and Drug Administration. Guidance for Industry – Characterization and Qualification of Cell Substrates and Other Biological Materials Used in the Production of Viral Vaccines for Infectious Disease Indications6World Health Organization. Guidelines on the Quality, Safety and Efficacy of Biotherapeutic Protein Products Prepared by Recombinant DNA Technology Fragments that short cannot carry a functional gene.
The FDA’s Vaccines and Related Biological Products Advisory Committee has evaluated the theoretical oncogenic risk of residual DNA and treats a frequency below one in ten million as the acceptable safety threshold. The 10-nanogram cap combined with the fragment-size limit keeps the calculated risk well below that line. Every vaccine’s package insert lists the cell substrates used during production along with residual materials, and those inserts are published by the FDA.
Vaccines That Avoid Human Cell Lines
Alternatives exist for some, but not all, of the affected vaccines.
- Most seasonal flu vaccines are still grown in fertilized chicken eggs.
- Flucelvax uses MDCK cells from canine kidney tissue. Some other vaccines use Vero cells from African green monkey kidney tissue.
- FluBlok (recombinant influenza) and Nuvaxovid (Novavax COVID-19) are made using insect cell platforms.4Centers for Disease Control and Prevention. Cell-Based Flu Vaccines
- Hepatitis B vaccines Recombivax and Engerix-B are produced in recombinant yeast.
There is no fetal-cell-free alternative currently available for the rubella component of MMR, for varicella, or for hepatitis A in the United States. If you want to know which of your scheduled doses have alternatives and which do not, ask your healthcare provider to walk through your specific list.
Religious Positions
Most major religious bodies distinguish between the original abortions decades ago and the ongoing use of the cell lines descended from them today. They differ on how much weight that distinction carries.
The Congregation for the Doctrine of the Faith issued a 2020 note concluding that receiving vaccines produced with fetal cell lines is “morally acceptable” when no ethically equivalent alternative is available, and that using such a vaccine “does not constitute formal cooperation with the abortion from which the cells used in production of the vaccines derive.”7The Holy See. Note on the Morality of Using Some Anti-Covid-19 Vaccines The note also urges manufacturers to develop alternatives and affirms that vaccination must remain voluntary.
The Australian Fatwa Council issued a 2021 ruling declaring COVID-19 vaccination permissible under Islamic law, noting that molecules from the descendant cell cultures do not make it into the final product.8Australian National Imams Council. Coronavirus (COVID-19) Vaccine Fatwa
The Southern Baptist Convention has maintained longstanding opposition to the destruction of human embryos for research, reaffirmed in a 1999 resolution that encouraged support for alternatives.9SBC.net. Resolution on Human Embryonic and Stem Cell Research The SBC has not issued a blanket prohibition on receiving vaccines made with historical fetal cell lines, and individual Southern Baptists hold a range of views.
Exemptions if You Object
If you object to fetal-cell-derived vaccines on religious or moral grounds, the pathways depend on the setting.
School Immunization
Nearly all states allow religious exemptions from school immunization requirements, and roughly sixteen states also permit broader philosophical or personal-belief exemptions. Procedures vary: some states accept a signed statement, others require a notarized affidavit, and a few require sign-off from a health official. Medical exemptions are available in every state for children who cannot safely receive a particular vaccine. Check your state health department’s current form before filing, because requirements change.
The Workplace
Title VII of the Civil Rights Act requires employers to provide reasonable accommodations for sincerely held religious beliefs, which can include exemptions from workplace vaccination mandates. The Supreme Court’s 2023 decision in Groff v. DeJoy raised the bar employers must clear to deny a religious accommodation: refusal is permitted only if the accommodation would impose a “substantial” burden on the business, considering cost, workplace safety, and impact on coworkers.10U.S. Equal Employment Opportunity Commission. Religious Discrimination The prior standard allowed denial for anything more than a trivial cost.
A religious objection does not have to align with the official teachings of any organized religion. The EEOC evaluates whether the belief is sincerely held, not whether it matches formal doctrine. Employers can ask follow-up questions to assess sincerity, and inconsistencies between the stated belief and your other medical decisions can undermine the request.