Legislators, ecologists, and medical and public health professionals became worried about environmental exposure to mercury in the late 1990s , especially from fish consumption. The U.S., with greater attention to documented and possible damaging consequences of such exposures, In 1999, the Food and Drug Administration (FDA) ordered drug makers to disclose the amount of mercury in their products.
The findings of mercury in thimerosal vaccines met the FDA recommendations for sensitivity to mercury present in seafood. Mercury in fish occurs in the form of methylmercury, which in the human body is not easily metabolised and excreted. It is understood that it induces damaging neurological symptoms at some degrees of high exposure.
The FDA has a dilemma: no guidelines were made regarding sensitivity to ethylmercury quantities. Should the recommendations on methylmercury be extended to ethylmercury? Is there reason for alarm about mercury toxicity in infant vaccines?
Along with the American Academy of Pediatrics and other organisations, unable to address these concerns instantly, they worked on vaccine makers to limit or avoid the use of thimerosal in vaccines. In addition, experiments were designed to investigate whether there were adverse effects on the level of mercury in vaccines in children exposed to them.
At this point, critics and others were concerned about the efficacy of thimerosal, positing that autism could be the result of mercury toxicity in vaccines. A thorough safety review of the topic was conducted by the Institute of Medicine. Currently, thimerosal is therefore no longer used in several paediatric vaccines, although the preservative may contain certain formulations of influenza vaccine available in multi-dose vials.