1929: Eli Lilly & Co. registers thimerosal under the trade name Merthiolate. It begins to appear in over-the-counter products and as an anti-bacterial preservative in multi-dose vaccines.
1974: Eli Lilly ceases production of vaccines. Several other pharmaceutical companies continue using thimerosal as a preservative in vaccines.
1980: The FDA begins a review of over-the-counter (OTC) products containing thimerosal.
1982: The FDA proposes a ban on thimerosal in OTC ointments, citing its possible toxicity and ineffectiveness.
January, 1991: The CDC's Advisory Committee on Immunization Practices adds Haemophilus influenzae B (Hib) to its recommendations for childhood immunization. Ten months later, they recommend Hepatitis B vaccinations for children. Thimerosal is used as a preservative in multidose vials of both vaccines.
November, 1997: Congress passes the Food and Drug Administration Modernization Act, requiring the study of mercury content in FDA-approved products. The review discloses the hitherto-unrecognized levels of ethylmercury in vaccines.
April, 1998: The FDA's proposed ban on thimerosal in OTC products goes into effect.
1999: Some public-health experts publicly advocate the removal of thimerosal from vaccines. Their recommendation is partly based on a study that found neurological problems in babies whose mothers had ingested mercury while eating whale blubber during pregnancy. This study becomes the source for the EPA's recommended limit for exposure to mercury.
July, 1999: Public-health officials announce that thimerosal will be phased out of vaccines. The CDC, American Academy of Pediatrics, and FDA insist the measure is purely precautionary. They ask manufacturers to eliminate or reduce mercury in vaccines as quickly as possible.
August, 1999: Congressman Dan Burton (R-Ind.), then-Chairman of the House Committee on Government Reform, begins hearings for what will become a three-year investigation into autism and its possible causal link to vaccines. At this time, federal agencies estimate that autism affects 1 in 500 children in the United States.
February, 2000: CDC researcher Thomas Verstraeten's analysis of CDC Vaccine Safety Datalink records finds a relative risk of 2.48 for autism in children who receive thimerosal-containing vaccines (TCVs).
June, 2000: Verstraeten discloses his analysis to vaccine advisory committee members at a meeting outside Atlanta. The relative-risk figure has dropped from 2.48 to 1.69. Later that month, the advisory committee decides against stating a preference against TCVs.
July, 2000: Safe Minds forms to "investigate and raise awareness of the risk to infants and children of exposure to mercury through medical products, including thimerosal in vaccines."
April, 2001: Sallie Bernard and Lyn Redwood publish "Autism: A Novel Form of Mercury Poisoning" in the journal Medical Hypotheses, publicizing the case for a causal link between mercury and autistic spectrum disorders. The same month, the Institute of Medicine (IOM) releases a report finding no association between the measles-mumps-rubella (MMR) vaccine and autism.
July, 2001: The CDC's vaccine advisory committee again decides not to state a preference for thimerosal-free vaccines. By this date, diptheria-tetanus-pertusis (DTaP), Hepatitis B, and Hib vaccines manufactured for the U.S. market no longer contain thimerosal. TCVs that have not yet expired may remain on doctors' shelves.
October, 2001: A second IOM report finds insufficient evidence to either accept or reject a causal relationship between TCVs and neurological disorders, but says the "hypothesis is biologically plausible."
July, 2002: Proceedings looking into the causal link between thimerosal and autism begin in the federal vaccine court. This is the first step in the legal process for parents seeking compensation for alleged adverse effects of vaccines on their children.
November, 2002: The FDA has estimated this as the final expiration date for thimerosal-containing HepB, Hib, and DTaP vaccines. A California study finds that a three-fold increase in classic autism diagnoses in the state between 1987 and 1998 is real, and cannot be explained as a result of improved diagnostic techniques and case-finding.
November, 2002: Congressional Republicans insert language into the 475-page homeland security bill that would prevent parents from suing vaccine makers. After public outcry, the proposal is scrapped in January 2003.
January, 2003: A CDC study finds a ten-fold increase in autism rates in Atlanta between the 1980s and 1996. Some researchers now estimate 1 in 150 children have autistic spectrum disorders.
June, 2003: an analysis of CDC vaccination data finds that children who received TCVs had a higher risk.
October, 2003: One of the largest, most comprehensive studies discounting a link between TCVs and neurological disorders is published by Danish researchers.
November, 2003: The House Committee on Government Reform's report on its investigation assails public-health officials and pharmaceutical companies for failing to remove ethylmercury, "a potent neurotoxin" from medical products. The report concludes: "Our public health agencies' failure to act is indicative of institutional malfeasance for self-protection and misplaced protectionism of the pharmaceutical industry."
November, 2003: Verstraeten's analysis is published in a peer-reviewed journal, Pediatrics, setting off a new wave of controversy and accusations of statistical manipulation. Congressman Dave Weldon (R-Fla.) writes to CDC Director Julie Gerberding to open up the agency's vaccination database to independent researchers.
November, 2003: A national autism summit is held in Washington D.C. to discuss an interagency effort to researching the causes and possible treatments for autism.
January, 2004: A joint statement by the AAP, American Academy of Family Physicians, the CDC vaccination advisory committee, and the Public Health Service maintains that "there remains no convincing evidence of harm caused by low levels of thimerosal in vaccines."
February, 2004: A panel sponsored by the Institute of Medicine convenes to examine the possible thimerosal-autism link. Its report is expected this spring.
- Rina Palta