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National Vaccine Program OfficeHHS Activities --- ThimerosalThimerosal has been used as an additive in vaccines since the 1930's because it is very effective in killing bacteria and preventing bacterial contamination in multi-dose containers. Thimerosal is an organo-mercurial (a derivative of ethyl mercury) and is approximately 50% mercury by weight. A different form of mercury - methyl mercury, which is found in seafood, has been associated with health effects - particularly in infants whose mothers were exposed to high doses during pregnancy and has led the USDA and FDA to recommend that pregnant women and infants limit their amount of food containing mercury. To date, thimerosal, in the amounts that have been present in vaccines, has not been demonstrated to result in adverse neurological effects. . Concern exists about the health effects of mercury of any sort, and the elimination of mercury from vaccines is judged a feasible means of reducing an infant's total exposure to mercury in a world where other environmental sources of exposure are more difficult or impossible to eliminate (for example, certain foods). Although the risk of harm is only theoretical, the public health service remains committed to working with industry to remove thimerosal from vaccines as a precautionary measure. HHS Activities The Department of Health and Human Services, through its agencies, is working to assess the potential impact of thimerosal, partner with industry in the development of vaccines that are thimerosal-reduced or thimerosal free, monitor the safety and long-term effects of vaccines containing thimerosal, and ensure a compensation program exists should harm be established. Since July 1999, efforts have been made to reduce the thimerosal content of vaccines. With the exception of influenza vaccines, at this time, all routinely recommended licensed pediatric vaccines that are currently being manufactured for the U.S. market contain no thimerosal or contain significantly reduced (e.g., trace amounts) of thimerosal. Vaccines that have never had thimerosal added or utilized as a preservative, but which contain trace amounts of thimerosal as a result of the production process (e.g., thimerosal is used to sterilize equipment) are typically characterized as "thimerosal preservative-free" vaccines. In the case of influenza vaccines, in the past two years manufacturers have developed and made available "thimerosal preservative free" influenza vaccines. In addition, HHS supports research to better understand the potential human health effects, if any, from exposure to thimerosal in vaccines. Two avenues of research have been pursued, one involving the use of clinical and laboratory information to examine the blood levels of mercury in children shortly after vaccination, and a second involving the use of epidemiologic information to examine health outcomes in children who have received thimerosal containing vaccines. The Centers for Disease Control and Prevention is the lead federal agency for protecting the health and safety of people by providing credible information to enhance health decisions, and promoting health through strong partnerships. CDC serves as the national focus for developing and applying disease prevention and control, environmental health, and health promotion and education activities designed to improve the health of the people of the United States. For more information about CDC activites and thimerosal see www.cdc.gov/nip. Vaccine Safety Datalinks Study - this project involves partnerships with seven large health maintenance organizations (HMOs) to continually monitor vaccine safety. VSD is an example of a large-linked database (LLDB) and includes information on more than six million people. All vaccines administered within the study population are recorded. Available data include vaccine type, date of vaccination, concurrent vaccinations (those given during the same visit), the manufacturer, lot number and injection site. Medical records are then monitored for potential adverse events resulting from immunization. Through this project the incidence of autism as a function of the amount of thimerosal a child received from vaccines has been studied. Results indicated no change in autism rates relative to the amount of thimerosal a child received during the first six months of life (from 0 micrograms to greater than 160 micrograms). A weak association was found with thimerosal intake and certain neurodevelopmental disorders (such as attention deficit hyperactivity disorder) in one study, but was not found in a subsequent study. Additional studies are underway. The Food and Drug Administration (FDA)- The FDA is responsible for overseeing product development, evaluation and regulation. The FDA is continuing its efforts to reduce the exposure of infants, children, and pregnant women to mercury from all sources. Discussions with the manufacturers of influenza virus vaccines (which are routinely recommended for pregnant women) regarding thimerosal-reduced and thimerosal-free presentations are ongoing. For additional information see the Food and Drug Administration/Center for Biologics Evaluation and Research - thimerosal page http://www.fda.gov/cber/vaccine/thimerosal.htm The Vaccine Adverse Event Reporting System (VAERS) was established in 1990 under the joint administration of CDC and the Food and Drug Administration (FDA) to accept reports of suspected adverse events after administration of any vaccine licensed in the United States. VAERS is a passive surveillance system: reports of events are voluntarily submitted by those who experience them, their caregivers, or others. NIH - The National Institute of Health supports both basic and applied research on infectious diseases and the development of new and improved vaccines Since 2000, the National Institute of Allergy and Infectious Diseases has supported research to determine if the guidelines developed for methyl mercury are appropriate for assessing the safety of thimerosal and to examine similarities and differences in distribution, metabolism, and excretion of thimerosal and methyl mercury. Results from some of this work suggest that there are differences in the way that thimerosal and methyl mercury are distributed, metabolized, and excreted. Thimerosal appears to be removed from the blood and body more rapidly than methyl mercury. Pichichero ME, Cernichiari E, Lopreiato J, and Treanor J. Mercury concentrations and metabolism in infants receiving vaccines containing thimerosal: a descriptive study. Lancet 360:1737-1741 (2002). The Lancet online: www.thelancet.com To learn more about NIH thimerosal research: HHS funded IOM studies Since 1999 CDC and NIAID have supported independent and expert evaluations for vaccine-safety questions. In conducting their review, the committee reads and discusses the relevant epidemiologic evidence for or against a causal relationship, as well as any case reports, and clinical evidence. The committee also hears presentations from the authors of key papers, as well as ongoing, unpublished research. Following each meeting, the committee writes a report with three types of conclusions about:
Thimerosal and Neurodevelopmental Disorders - October 2001 Meeting The Committee did conclude that the hypothesis that exposure to thimerosal-containing vaccines could be associated with neurodevelopmental disorders was biologically plausible. To read the report and information presented at the meeting click here http://www.iom.edu/event.asp?id=6694 Vaccines and Autism - February 2004 Meeting Frequently asked Questions about Thimerosal FDA frequently asked questions about thimerosal http://www.fda.gov/cber/vaccine/thimfaq.htm CDC frequently asked questions about thimerosal http://www.cdc.gov/nip/vacsafe/concerns/thimerosal/faqs-mercury.htm Reports and statements about thimerosal Food and Drug Administration/Center for Biologics Evaluation and Research - Thimerosal http://www.fda.gov/cber/vaccine/thimerosal.htm Nov. 5, 1999 MMWR - Recommendations Regarding the Use of Vaccines That Contain Thimerosal as a Preservative - http://www.cdc.gov/mmwr/preview/mmwrhtml/mm4843a4.htm |
Last revised: September 7, 2004
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