Formaldehyde has a long history of use in the manufacture of certain viral and bacterial vaccines. It is used to inactivate viruses (e.g., influenza, polio) and to detoxify bacterial toxins, such as the toxin used to make diphtheria vaccine. Formaldehyde is diluted during the manufacturing process, but residual quantities of formaldehyde may be found in some current vaccines. The average quantity of formaldehyde to which a young infant could be exposed to at one time through vaccines is very small and is considered to be safe. Although high concentrations of formaldehyde can damage DNA (the building block of genes) and cause cancerous changes in cells in the laboratory,
In addition, quantities of formaldehyde at least 600-fold greater than that contained in vaccines have been found to be safe in animals.
However, this is, apparently, founded in some sort of fact:
"In weighing how to handle the issue, Georgetown looked to the debate of a decade ago, when many Catholics became aware that cells from an aborted fetus were used to originate cultures used to manufacture chicken pox vaccine and measles-mumps-rubella vaccine. Since then, a measles-mumps-rubella vaccine has been developed without cells from an aborted fetus, but the chicken pox vaccine is still made with the same cell line. "
I.E., an aborted fetus' cell line was used to develop the vaccine in the first place.
That is: they do not use NEW aborted tissue to produce the chickenpox vaccine.
Human Fetal Diploid Cells
Human diploid cells are batches of human cells that are grown in a laboratory. Unlike cancer cells, they have the same number of chromosomes as normal human cells.
Certain diploid cell strains are valuable in vaccine manufacture because these cells can be used for a very long period of time in the laboratory and are a reliable means by which many viruses that infect humans can be successfully and easily grown. Vaccines prepared in human diploid cells have proven to be very safe over the past several decades.
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.123. 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.
These two cell strains have been growing under laboratory conditions for more than 35 years. The cells are merely the biological system in which the viruses are grown.
The cells reproduce themselves, so there is no need to abort additional fetuses to sustain the culture supply. Viruses are collected from the diploid cell cultures and then processed further to produce the vaccine itself.
My moral ethics aside (which I will not discuss because of BYC rules): I like the idea these two lost babies have saved countless lives.
http://www.immunizationinfo.org/issues/vaccine-components/human-fetal-links-some-vaccines