Thimerosal (Thiomersal) in Vaccines
Frequently Asked Questions

• How does the FDA evaluate vaccines to make sure they are safe?

   

• What are preservatives and why are they added to vaccines?

   

• What is thimerosal?

   

• What has the FDA done to address the issue of mercury containing preservatives in vaccines?

   

• Why did the FDA wait until mandated by Congress under FDAMA 1997 to examine the use of preservatives containing mercury?

   

• What progress has been made towards the goal of eliminating thimerosal from vaccines?

   

• Why are some vaccines noted to be "thimerosal-free" while some are "thimerosal-reduced"? What is the difference between "thimerosal-free" and "preservative-free"?

   

• Why is exposure to mercury a concern?

   

• Is mercury from thimerosal a major source of mercury exposure in infants?

   

• I understand that the Institute of Medicine (IOM) recently reviewed the issue of thimerosal in vaccines. What were the IOM's findings?

   

• The IOM recommends the use of thimerosal-free DTaP, hepatitis B, and Hib vaccines in the United States, despite the fact that there might be remaining supplies of thimerosal-containing vaccines available. Why doesn't the FDA recall all thimerosal-containing vaccines intended for use in infants and small children?

   

• The IOM urged that "full consideration be given to removing thimerosal from any biological product to which infants, children, and pregnant women are exposed." (IOM 2001) Routine administration of influenza vaccine is recommended in pregnant women, yet currently available U.S. licensed influenza vaccines contain thimerosal. Why are pregnant women receiving influenza vaccine containing thimerosal?

   

• Although thimerosal is no longer used as a preservative in routinely recommended childhood vaccines manufactured in the US, what is being done about the thimerosal content of less commonly administered vaccines and other biological products given to infants, children, and pregnant women?

   

• When thimerosal was removed as a preservative in vaccines, what replaced it? How do we know that the new formulations are safe?

   

• What kind of evidence would be needed to demonstrate that autism or other neurodevelopmental disorders are caused by exposure to thimerosal?

   

• How can these considerations applied when assessing whether autism is caused by thimerosal?

   

• Some individuals have pointed out that the clinical features of individuals with autism are similar to those found following mercury poisoning. Does this indicate that autism is caused by exposure to mercury?

   

• Does the available evidence address the possibility that exposure to thimerosal causes a particular type of autism, termed "regressive autism" in a subset of genetically susceptible children?

   

• Central nervous system lesions and neurochemical abnormalities following exposure to mercury have been compared to that found in individuals with autism. Do these studies prove that the organic mercury metabolite of thimerosal (ethylmercury) found in some vaccines can cause autism?

   

• Is it possible that genetic and non-genetic factors establish a predisposition among some children to adverse effects from thimerosal?

   

• Could there be a subset of genetically susceptible children predisposed to develop autism following exposure to thimerosal?

   

• Autism and autism-spectrum disorders have been steadily increasing, especially during the 80's and 90's. During this time period the number of vaccines that children have received has more than tripled. Doesn't this implicate vaccinations as a cause of autism?

   

• Is it true that some autistic children experience neurobehavioral improvements after chelation therapies? Doesn't this prove that mercury causes autism if autistic children improve after chelation?

   

• What can you tell me about other additives to vaccines besides preservatives?

  Bibliography