ARCHIVED - Updated Recommendations on the use of Thimerosal-Containing Vaccines in Canada


Canada Communicable Disease Report
Volume 31 • ACS-12
1 December 2005

An Advisory Committee Statement (ACS)
National Advisory Committee on Immunization (NACI)*?

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4 Pages - 200 KB



The National Advisory Committee on Immunization (NACI) provides the Public Health Agency of Canada with ongoing and timely medical, scientific, and public health advice relating to immunization. The Public Health Agency of Canada acknowledges that the advice and recommendations set out in this statement are based upon the best current available scientific knowledge and is disseminating this document for information purposes. People administering the vaccine should also be aware of the contents of the relevant product monograph(s). Recommendations for use and other information set out herein may differ from that set out in the product monograph(s) of the Canadian manufacturer(s) of the vaccine(s). Manufacturer(s) have sought approval of the vaccine(s) and provided evidence as to its safety and efficacy only when it is used in accordance with the product monographs. NACI members and liaison members conduct themselves within the context of the Public Health Agency of Canada's Policy on Conflict of Interest, including yearly declaration of potential conflict of interest.  


NACI previously published evidence-based recommendations regarding the use of vaccines containing the mercury-based preservative thimerosal(1). Since that time new data have been published(2-5) and considered in depth by the Institute of Medicine (IOM) Immunization Safety Review Committee(6). The IOM is an independent, scientific advisory body that reviews evidence and provides advice concerning significant public health policy issues. Members of the Safety Review Committee were chosen not only for their expertise but also for their lack of any real or perceived conflicts of interest. In their detailed report, released in April 2004, the Immunization Safety Review Committee summarized their conclusions and made the following recommendations:

  • "Thus, based on this body of evidence, the committee concludes that the evidence favors rejection of a causal relationship between thimerosal containing vaccines and autism. "

  • "At this time, the committee does not recommend a policy review of the current schedule and recommendations for the administration of routine childhood vaccines based on hypotheses regarding thimerosal and autism. "

  • "Given the lack of direct evidence for a biological mechanism and the fact that all well-designed epidemiological studies provide evidence of no association between thimerosal and autism, the committee recommends that cost-benefit assessments regarding the use of thimerosal-containing versus thimerosal-free vaccines and other biological or pharmaceutical products, whether in the United States or other countries, should not include autism as a potential risk. "

Additional studies(7,8) published after the IOM deliberations and expert reviews(9-12) fully support these conclusions.


Currently, in Canada, some multidose preparations of influenza or hepatitis B vaccines are the only thimerosal-containing products that might be offered to children as part of the routine childhood immunization schedule. Thimerosal-free influenza and hepatitis B vaccines have also become available in recent years. NACI will prepare a full revised statement regarding thimerosal in vaccines to replace its previous statement published in 2003(1).

However, as the annual influenza vaccine campaign is getting under way, and questions as to the preference of one product over another are bound to arise, NACI has revisited the issue and makes the following recommendations:

  • There is no legitimate safety reason to avoid the use of thimerosal-containing products for children or older individuals, including pregnant women.

  • The only absolute contraindication related to the thimerosal component of some vaccines is a previous episode of anaphylaxis attributed to thimerosal. While one such case has been described, the link to thimerosal was not proven.

  • If there is a documented history of a delayed hypersensitivity reaction to thimerosal (as manifest by a large local reaction with an eczematous rash) or a positive patch test reaction to thimerosal, immunization with thimerosal-containing vaccines can proceed, but individuals should be advised to report any reaction of concern following immunization so that it can be managed appropriately.

  • The long-term goal of removing thimerosal from vaccines, provided there are safe alternatives to ensure sterility in multidose vials, still applies, since this is one achievable way to reduce total environmental exposure to mercury.


Public confidence in vaccines and high rates of vaccine uptake are critical to the continued effectiveness of immunization programs. Even when risks are purely theoretical, experience has shown that unaddressed public concerns can drastically decrease immunization coverage, to the detriment of public health. Thus the call to remove thimerosal from vaccines seeks to maintain public confidence by avoiding even theoretical risk. NACI makes recommendations based on the best available scientific evidence. Vaccine safety is an essential consideration in any recommendation made by NACI. Concerns regarding thimerosal, as reviewed in the 2003 statement, were purely theoretical. Nevertheless, NACI identified them as important issues for further consideration and study. The weight of evidence now available, however, refutes any link between thimerosal and autism. As such, NACI concludes that there is no reason for vaccine providers or other health care professionals who may counsel individuals regarding immunization to raise any concerns regarding exposure to thimerosal.


  1. National Advisory Committee on Immunization. Statement on thimerosal. CCDR 2003;29(ACS-1):1-10.

  2. Hviid A, Stellfeld M, Wohlfahrt J et al. Association between thimerosal-containing vaccine and autism. JAMA 2003;290(13):1763-66.

  3. Verstraeten T, Davis RL, DeStefano F et al. Vaccine Safety Datalink Team. Safety of thimerosal-containing vaccines: a two-phased study of computerized health maintenance organization databases. Pediatrics 2003;112(5):1039-48.

  4. Madsen KM, Lauritsen MB, Pedersen CB et al. Thimerosal and the occurrence of autism: Negative ecological evidence from Danish population-based data. Pediatrics 2003;112(3 Pt 1):604-6.

  5. Stehr-Green P, Tull P, Stellfeld M et al. Autism and thimerosal-containing vaccines: Lack of consistent evidence for an association. Am J Prev Med 2003;25(2):101-6.

  6. Institute of Medicine. Immunization safety review: Vaccines and autism. National Academy Press, 2004.

  7. Heron J, Golding J and the ALSPAC Study Team. Thimerosal exposure in infants and developmental disorders: A prospective cohort study in the United Kingdom does not support a causal association. Pediatrics 2004;114:577-83. URL: .

  8. Andrews N, Miller E, Grant A et al. Thimerosal exposure in infants and developmental disorders: A retrospective cohort study in the United Kingdom does not support a causal association. Pediatrics 2004;114:584-91. URL: .

  9. Parker SK, Schwartz B, Todd J et al. Thimerosal-containing vaccines and autistic spectrum disorder: Critical review of published original data. Pediatrics 2004;114:793-804. URL: .

  10. Clements CJ. The evidence for the safety of thimerosal in newborn and infant vaccines. Vaccine 2004;22:1854-61.

  11. Nelson KB, Bauman ML. Thimerosal and autism. Pediatrics 2003;111:674-9.

  12. World Health Organization. Global Advisory Committee on Vaccine Safety, 9-10 June, 2005. WHO Wkly Epidemiol Rec 2005;80:244-5.


* Members: Dr. M. Naus (Chair), Dr. T. Tam (Executive Secretary), Dr. S. Dobson, Dr. B. Duval, Dr. J. Embree, Ms. A. Hanrahan, Dr. J. Langley, Dr. A. McGeer, Dr. K. Laupland, Dr. M-N Primeau, Dr. B. Tan, Dr. B. Warshawsky.  

Liaison Representatives: S. Callery (CHICA), Dr. J. Carsley (CPHA), Dr. A. Mawle (CDC), Dr. D. Money (SOGC), A. Honish (CNCI), Dr. B. Larke (CCMOH), Dr. B. Law (ACCA), Dr. M. Salvadori (AMMI Canada), Dr. S. Rechner (CFPC), Dr. J. Salzman (CATMAT), Dr. L. Samson (CPS), Dr. D. Scheifele (CAIRE).

Ex-Officio Representatives: Dr. S. Deeks (CIDPC), Dr. H. Rode (BGTD), Dr. M. Lem (FNIHB), Dr. M. Tepper (DND).  

?This statement was prepared by Dr. Barbara Law and was approved by NACI and the Public Health Agency of Canada.

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