However, the difference between vaccination and natural infection is the price paid for immunity. The price paid for immunity after natural infection might be pneumonia from chickenpox, mental retardation from Hib, pneumonia from pneumococcus, birth defects from rubella, liver cancer from hepatitis B virus, or death from measles. A. Preservatives are included in some vaccines to prevent vaccines from becoming contaminated by bacteria. Because bacteria cannot grow in the presence of preservatives, children are protected against bacteria that could inadvertently enter the bottle containing vaccine. One preservative contained in some vaccines is called thimerosal.
Thimerosal contains mercury.
Several studies have shown that when pregnant women ingest large quantities of mercury that are found in heavily contaminated fish, the developing fetus may be affected and later be found to have neurological disturbances. Recent studies by the National Institutes of Health showed that the levels of mercury contained in the blood of immunized children are similar to those in unimmunized children. So they recommended that thimerosal be removed from vaccines. The result is that all routinely recommended vaccines should be free of thimerosal by the Spring of 2001. Carefully performed studies disprove the notion that autism is caused by the MMR vaccine.