The Agency has been working with other PHS agencies, the American Academy of Pediatrics and manufacturers, particularly those that manufacture childhood vaccines, to eliminate thimerosal from vaccines and to further evaluate the potential health effects of thimerosal. The vaccine may be a liquid preparation in a suspending fluid such as buffered saline. At present, the only adjuvants that are found in U.S. licensed vaccines are the aluminum salts. There are four preservatives that are currently contained in U.S. licensed vaccines. Thimerosal contains mercury in the form of ethyl mercury.
Thimerosal is the most widely used preservative in vaccines.
Disease outbreaks have occurred following contamination of multi-dose vaccine vials. Humans may be exposed to organic mercury in the form of methyl mercury from eating contaminated fish. Very high levels of mercury are toxic. Because mercury is found naturally in the environment, it is not possible to prevent all exposure to mercury, however, the industrial uses and releases of mercury have been reduced very substantially in recent decades in the U.S. and most other industrialized countries. Although mercury is found in the environment, in food and in household products, exposure to mercury is of concern and, when possible, should be avoided.