There are three cell lines, derived from three abortions, that are involved in vaccine manufacture. From the National Network for Immunization Information (NNii): Immunization Issues: Human Fetal Links with Some Vaccines

Two different strains of human diploid cell cultures made from fetuses have been used extensively for vaccine production for decades. One was developed in the United States in 1961 (called WI-38) and the other in the United Kingdom in 1966 (called MRC-5).

WI-38 came from lung cells from a female fetus of 3-months gestation and MRC-5 was developed from lung cells from a 14-week-old male fetus. Both fetuses were intentionally aborted, but neither was aborted for the purpose of obtaining diploid cells. The fetal tissues that eventually became WI-38 and the MRC-5 cell cultures were removed from fetuses that were dead. The cellular biologists who made the cell cultures did not induce the abortions.

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The virus that led to the only rubella vaccine available in the United States and that is widely used overseas (Meruvax II, Merck) came from tissues obtained at the time of an abortion performed on a rubella virus-infected mother.  The abortion was not conducted in order to isolate the virus, but rather because the mother and the fetus were infected with wild rubella virus that posed a risk of major birth defects.

Since that wild strain of rubella virus (known as RA27/3) was isolated, it has been grown in human fetal diploid cells. There is no need to obtain additional cells from aborted fetuses to sustain the supply of attenuated rubella viruses used to manufacture additional batches of rubella vaccine for the future.

During the development of the present rubella vaccine, cells from animals other than humans were also studied for vaccine manufacture but these proved to be less safe and/or less effective than the RA27/3 vaccine grown in WI-38 cells.

According to the PONTIFICIA ACADEMIA PRO VITA, (pdf file downloaded from NCBF Vatican Response) an English translation of a commentary which appeared in Italian in the scholarly journal Medicina e Morale, as of 2005 the following vaccines are manufactured using the cell lines  WI-38, MRC-5 and or RA 27/3.

 A) Live vaccines against rubella:

• the monovalent vaccines against rubella Meruvax® (Merck) (U.S.), Rudivax® (Sanofi Pasteur, Fr.), and Ervevax® (RA 27/3) (GlaxoSmithKline, Belgium);
• the combined vaccine MR against rubella and measles, commercialized with the name of M-R-VAX® (Merck, US) and Rudi-Rouvax® (AVP, France);
• the combined vaccine against rubella and mumps marketed under the name of Biavax® (Merck, U.S.),
• the combined vaccine MMR (measles, mumps, rubella) against rubella, mumps and measles, marketed under the name of M-M-R® II (Merck, US), R.O.R.®, Trimovax® (Sanofi Pasteur, Fr.), and Priorix® (GlaxoSmithKline UK).

B) Other vaccines, also prepared using human cell lines from aborted foetuses:

• two vaccines against hepatitis A, one produced by Merck (VAQTA), the other one produced by GlaxoSmithKline (HAVRIX), both of them being prepared using MRC-5;
• one vaccine against chicken pox, Varivax®, produced by Merck using WI-38 and MRC-5;
• one vaccine against poliomyelitis, the inactivated polio virus vaccine Poliovax® (Aventis-Pasteur, Fr.) using MRC-5;
• one vaccine against rabies, Imovax®, produced by Aventis Pasteur,  MRC-5 strain;
• one vaccine against smallpox, AC AM 1000, prepared by Acambis using MRC-5, which as of 2005 was still on trial.

The National Catholic Bioethics Center (NCBF) on the Pontifical Academy for Life Statement regarding the Use of Vaccines

From the FAQ:

What is the Church's teaching about the use of certain vaccines that have a distant historical association with abortion?

There are a number of vaccines that are made in descendent cells of aborted fetuses. Abortion is a grave crime against innocent human life. We should always ask our physician whether the product he proposes for our use has an historical association with abortion. We should use an alternative vaccine if one is available.

What does it mean when we say that these products are made in "descendent cells"?

Descendent cells are the medium in which these vaccines are prepared. The cell lines under consideration were begun using cells taken from one or more fetuses aborted almost 40 years ago. Since that time the cell lines have grown independently. It is important to note that descendent cells are not the cells of the aborted child. They never, themselves, formed a part of the victim's body.