In some cases, women who were infected with rubella while pregnant terminated their pregnancies due to the serious risks from CRS.

Following one such abortion, the fetus was sent to Plotkin at the laboratory he had devoted to rubella research. Testing the kidney of the fetus, Plotkin found and isolated the rubella virus. Separately, Leonard Hayflick (also working at the Wistar Institute at that time) developed a cell strain called WI-38 using lung cells from an aborted fetus. Hayflick found that many viruses, including rubella, grew well in the WI-38, and he showed that it proved to be free of contaminants and safe to use for human vaccines.

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The WI-38 cell strain was developed in 1962 in the United States, and the MRC-5 cell strain (also started with fetal lung cells) was developed, using Hayflick’s technology, in 1970 at the Medical Research Center in the United Kingdom. It should be noted that Hayflick’s methods involved establishing a huge bank of WI-38 and MRC-5 cells that, while not capable of infinitely replicating like immortal cell lines, will serve vaccine production needs for several decades in the future.

The vaccines below were developed using either the WI-38 or the MRC-5 cell strains.

• Hepatitis A vaccines [VAQTA/Merck, Havrix/GlaxoSmithKline, and part of Twinrix/GlaxoSmithKline]
• Rubella vaccine [MERUVAX II/Merck, part of MMR II/Merck, and ProQuad/Merck]
• Varicella (chickenpox) vaccine [Varivax/Merck, and part of ProQuad/Merck]
• Zoster (shingles) vaccine [Zostavax/Merck]
• Adenovirus Type 4 and Type 7 oral vaccine [Barr Labs] *
• Rabies vaccine [IMOVAX/Sanofi Pasteur] *