Vaccines for varicella (chickenpox), rubella (the “R” in the MMR vaccine), hepatitis A, rabies (one version, called Imovax) and COVID-19 (Johnson & Johnson (J&J)/Janssen, which is no longer used in the U.S.) are all made by growing the viruses in fetal cells.

Why are fetal cells used to make some vaccines?

Viruses reproduce in cells, so to grow viruses for a vaccine, one of the necessary “tools” is a type of cell in which the virus will grow. Viruses will not grow in just any cell type, so one of the first things a scientist needs to do is to figure out what cells the virus will infect in the lab. Because viruses infect people, human cells are a good place to start checking.

The most important benefit offered by using fetal cells was that they were isolated from the sterile environment of the womb. This meant the cells would not be infected with other viruses, and the vaccine produced in these cells would not inadvertently introduce any other viruses.

To find out more about the decision to use fetal cells to grow vaccine viruses, check out the video, Stanley Plotkin: Pioneering the use of fetal cells to make rubella vaccine.

What types of fetal cells are used?

All vaccines made using fetal cells, except the COVID-19 vaccine, are made using fibroblast cells. The COVID-19 vaccine (J&J/Janssen) is made using fetal retinal cells.

Fibroblast cell history

Fibroblast cells are the cells needed to hold skin and other connective tissue together. The fetal fibroblast cells used to grow vaccine viruses were first obtained from elective termination of two pregnancies in the early 1960s. These same fetal cells obtained from the early 1960s have continued to grow in the laboratory and are used to make vaccines today. No further sources of fetal cells are needed to make these vaccines.

The reasons that fetal cells were originally used included:

• Viruses need cells to grow and tend to grow better in cells from humans than animals (because they infect humans).
• Almost all cells die after they have divided a certain number of times; scientifically, this number is known as the Hayflick limit. For most cell lines, including fetal cells, it is around 50 divisions; however, because fetal cells have not divided as many times as other cell types, they can be used longer. In addition, because of the ability to maintain cells at very low temperatures, such as in liquid nitrogen, scientists are able to continue using the same fetal cell lines that were isolated in the 1960s.

As scientists studied these viruses in the lab, they found that the best cells to use were the fetal cells mentioned above. When it was time to make a vaccine, they continued growing the viruses in the cells that worked best during these earlier studies.

Retinal cell history

The retinal cells used to make the COVID-19 adenovirus vaccine (J&J/Janssen) were isolated from a terminated fetus in 1985 and adapted for use in growing adenovirus-based vaccines in the late 1990s.

Adenovirus-based vaccines that cannot replicate when administered to people need to be produced in cells that have the necessary gene to allow for large quantities of the virus to be made. The retinal cell line, called PER.C6, was adapted to enable production of these altered viruses.

Find out more in this Vaccine Update article.

Other questions you may have about the use of fetal cells and vaccines

Can vaccines made using fetal cells alter a person’s DNA?

Even though fetal cells are used to grow vaccine viruses, vaccines do not contain these cells or pieces of DNA that are recognizable as human DNA. People can be reassured by the following:

• When viruses grow in cells, the cells are killed because in most cases the new viruses burst the cells to be released.
• Once the vaccine virus is grown, it is purified, so that cellular debris and growth reagents are removed.
• During this process of purification, any remaining cellular DNA is also broken down. To learn more about DNA and vaccine, visit the “Vaccine ingredients – DNA” page.

Do vaccines contain parts of fetuses or fetal cells?

In order to grow viruses in the lab, cells need to be made into single cell suspensions, meaning they can no longer be grouped together in the form of tissues or organs. As such, vaccines do not contain “parts of fetuses.”

Vaccines also do not contain fetal cells. Once the vaccine viruses are grown in the cells, the next step in the manufacturing process is to purify the vaccine viruses away from the cells and substances used to help cells grow. If you have ever picked blueberries, you can think of this part of the process as similar. While you are picking, you might get some of the blueberry plant — stems, leaves and even branches — in your berry bucket, but to use the berries, you remove all of those things, so your pie contains only the blueberries (and any other ingredients you choose to add).

This purification part of the process is important for two reasons. The first, and perhaps most obvious, is the manufacturing reason. From a manufacturer’s perspective, an efficient process that results in the purest possible product makes the final product easier to characterize. However, as consumers, the second, and more important, reason matters more. A pure product will not introduce unnecessary components that could trigger immune responses or affect us in other ways.

How can cells from the 1960s still be used today?

Cells grown in a laboratory setting are provided with an environment conducive to growth. As the cells reproduce and fill the container in which they are grown, researchers care for them by putting them in new containers and giving them additional nutrients to enable continued growth. As a result, the cells are able to replicate exponentially. Periodically, a portion of the cells will be frozen in liquid nitrogen for long-term storage. The extremely cold temperatures of liquid nitrogen freezers, around -200° C, cause biological activity to cease without killing the cells. Decades later, the cells, if thawed and provided with the appropriate nutrients and environment, will begin to grow again. As the cells grow, the newly produced cells can also be frozen, and the process extended again.

To read more about how this process is done in the laboratory, check out the article about Dr. Plotkin’s work on the Hilleman Film website.

Do more abortions need to be done?

No. Because the cells isolated in the 1960s have been cared for as described above, vaccine manufacturers do not need to seek new cell sources.

My religion is against abortions, so I don’t want to get these vaccines. Are alternatives available?

An alternative version of rabies vaccine is available; however, that is not the case for the rubella, chickenpox and hepatitis A vaccines.

Religious leaders from the major religions, including Catholicism, have evaluated the use of these cells in making vaccines and determined that it is not sinful to accept vaccines made in this manner.

To read more about religious positions related to vaccines, including the use of fetal cells, visit the Immunization Action Coalition’s “Religious Concerns” webpage.

Resources for additional information

Videos

• Stanley Plotkin: Pioneering the use of fetal cells to make rubella vaccine
• Are Fetal Cells Used to Make Vaccines?

Webpages

• Vaccine Ingredients — DNA
• Religious Concerns: Resources & Information on the Immunize.org website

Books

• The Vaccine Race, by Meredith Wadman — Read a summary of the book and find how to get it in this article from the Vaccine Update newsletter.
• Vaccines and Your Family: Separating Fact from Fiction — See an excerpt, including information related to fetal cells, in this booklet.

Reference

Offit PA and Moser CA. Vaccines and Your Family: Separating Fact from Fiction. 2024. Columbia University Press.

Reviewed by Paul A. Offit, MD, on January 16, 2024