Varicella (chickenpox), rubella (the “R” in the MMR vaccine), hepatitis A, and one preparation of rabies vaccine are all made by growing the viruses in fetal embryo fibroblast cells. Fibroblast cells are the cells needed to hold skin and other connective tissue together. The fetal embryo fibroblast cells used to grow vaccine viruses were first obtained from elective termination of two pregnancies in the early 1960s. These same embryonic 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.

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 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.

Learn more about fetal tissues used in vaccines by watching this short video, part of the Talking about Vaccines with Dr. Paul Offit video series.

For a more detailed description of the history related to the use of fetal cells, please read our article about the book, The Vaccine Race, by Meredith Wadman from the April 2017 Vaccine Update.

For an interview about the use of fetal cells to make the rubella vaccine, view this video interview, Stanley Plotkin: Pioneering the use of fetal cells to make rubella vaccine.

Reference

Offit PA and Moser CA. Vaccines and Your Child: Separating Fact from Fiction. 2011. Columbia University Press.