NNii Offers Scientific View on Thimerosal and Vaccines


Diana Olson - (703) 299-0201

April 26, 2006

The National Network for Immunization Information (NNii) offers the following perspective for those who continue to have questions about thimerosal, a preservative formerly used in most vaccines:

  • Extensive evidence does not support a link between vaccines and autism. This evidence is based on well-established scientific studies conducted by independent investigators, in multiple locations, and who examined large numbers of children.
  • Immunization remains one of the most important things parents can do to protect their children from serious infectious diseases.
  • There has been no thimerosal preservative in US-licensed vaccines given to children less than 6 months of age since early 2003—the amount was greatly reduced by 2001. There is no evidence that there has been a reduction of cases of autism since thimerosal was removed from vaccines administered to children less than 6 months of age.
  • With no scientific evidence that thimerosal preservative in vaccines causes harm (except rare allergic reactions), many other countries continue to utilize thimerosal preservative-containing vaccines to be able to safely administer vaccines using multiple dose vials.
  • The only vaccine routinely recommended for administration to US children that may contain thimerosal preservative is trivalent inactivated influenza vaccine (TIV). TIV is not administered to children less than 6 months of age because they have a poor immune response to this vaccine. TIV is also available without thimerosal preservative. 
  • Tetanus toxoid (TT), and diphtheria and tetanus toxoids (DT for children <7 years of age and Td for children >7 years of age) may contain thimerosal as a preservative. Most children will receive thimerosal-preservative free DTaP and Tdap and will not receive TT, DT, or Td. DT is occasionally administered to young infants who cannot receive the acellular pertussis components of the usually used DTaP vaccines. Depending on the child’s age and the specific circumstances, TT or Td may be occasionally administered to children. Both DT and Td are available without thimerosal preservative.
  • The amount of thimerosal in TIV or in TT, DT, or Td is not considered a health risk.

Legislation has been introduced in Congress and several States that would limit access to vaccines containing thimerosal. Multiple scientific and medical organizations have written a letter1 expressing their concern that such legislation perpetuates false and misleading information about vaccine safety and would limit critical vaccine supply both in the United States and other countries.

The NNii media office has scientific experts available to discuss these issues. Contact Diana Olson at (703) 299 0201 to schedule an interview.

For more information, visit

Non-technical but evidence-based information about this topic can be found on the following links:

  • Descriptions of Vaccines and the Diseases they prevent
  • Scientific Studies on Thimerosal and Autism
  • What is Thimerosal, and why is it in Some Vaccines
  • A Report by the Institute of Medicine on “Vaccines and Autism”
  • Vaccine Misinformation
  • Cause or Coincidence
  • Evaluating Information About Vaccines on the Internet [This article is also available in print and is appropriate for distribution to patients. It is available at]

The National Network for Immunization Information (NNii) provides up-to-date, science based information about immunizations to health professionals, the public, policymakers, and the media. NNii is based at the University of Texas Medical Branch in Galveston and is affiliated with the Infectious Diseases Society of America, the Pediatric Infectious Diseases Society, the American Academy of Pediatrics, the American Nurses Association, the American Academy of Family Physicians, the National Association of Pediatric Nurse Practitioners, and the American College of Obstetricians and Gynecologists.