Immunization Program

Thimerosal and Vaccine

Questions and Answers

 

Q 1. What is Thimerosal?

A. Thimerosal is a very effective preservative that contains mercury and has been used in some vaccines and other products since the 1940s. Thimerosal is the most widely used preservative in vaccines. The FDA estimates that it is used in more than 30 licensed vaccines and biologics. Mercury is excreted from the body over time.

Q 2. Why is Thimerosal used in vaccines?

A. Thimerosal is used as an extra safeguard against contamination. It may be used during processing or added to the final container to prevent contamination when multi-dose vials are opened. Before Thimerosal was marketed in the United States, a number of safety studies were conducted, first on animals and then on humans.

Thimerosal is an important preservative that protects vaccine against bacterial contamination. Disease outbreaks have occurred following contamination of multi-dose vaccine vials in the United States and from other countries. For example, in April, 1995, three infants died in India from toxic shock syndrome after administration of contaminated measles vaccine at one health center.

Q3. Can all vaccines be made Thimerosal-free, or within accepted guidelines? If so, how quickly?

A. All vaccines either do not contain thimerosal or contain thimerosal within FDA guidelines. To further increase the margin of safety that already exists, clinicians can use the inherent flexibility in the current immunization schedule to fully vaccinate children and meet even the most conservative guidelines for cumulative mercury exposure. However, exposure to any form of mercury from any source should be minimized and Public Health Service agencies are working with private physician groups and vaccine manufacturers to expedite the process to reduce or eliminate thimerosal from vaccines used in the United States.

Q4. What could happen if parents ignored recommendations to use thimerosal-containing vaccines during this transition period?

A. Children would be at very real risk from illnesses that can be prevented with safe and effective vaccinations. High rates of vaccination led to declines of 95% to 100% in the occurrence of vaccine preventable diseases in the United States. Despite this, the pathogens responsible for most vaccine preventable diseases still circulate and rates of disease would increase if vaccine coverage dropped. For example, if vaccination coverage among infants dropped from 95% to 70%, an additional 2,500 cases of pertussis would be expected to occur. Moreover, the risk of death from pertussis is greatest in young children. A second severe vaccine preventable disease among young children is Haemophilus influenzae type b (Hib). Before vaccine was introduced, this pathogen was the leading cause of meningitis and other severe invasive infections among children; now cases of invasive Hib disease have virtually disappeared. If vaccination for Hib declined to 70%, 2,000 excess cases would occur with 1,200 cases of meningitis, resulting in about 100 deaths and 180 children who would suffer mental retardation and hearing loss.

Q5. If patients have a choice of vaccines, one with mercury or one without, which should they choose?

A. The most important thing is that parents not miss an opportunity to get their child immunized. We encourage parents to talk to their doctors. Every vaccine licensed by the FDA either contains no mercury or contains acceptable levels of thimerosal. Today, we’re discussing a minimal, if any, risk from minute levels of mercury-containing thimerosal versus the large and devastating risk of childhood diseases like bacterial meningitis and whooping cough if parents and physicians abandon vaccination during this transition period. Any missed vaccinations puts children at risk from disease.

Q6. Why isn’t the federal government just recommending not using vaccines with thimerosal in them if there is concern?

A. Making vaccines safer and more effective is a constant goal for the federal government. No vaccine is 100 percent safe or effective. Decisions must be based on weighing risks and benefits of each vaccine. Today, we’re discussing a minimal, if any, risk from minute levels of mercury-containing thimerosal versus the large and devastating risk of childhood diseases like bacterial meningitis and whooping cough if parents and physicians abandon vaccination during this transition period. Any missed vaccinations puts children at risk from disease.

Q7. How much mercury did my 6-month-old get in the last six months from vaccines? How dangerous is that?

A. Each dose of vaccine given your child met FDA requirements and should not be a concern to you now--your choice to vaccinate your baby was a sound one. The mercury levels being discussed are well within the safety margins; however, we are working toward further increasing the margin of safety that already exists. It is important that we limit the cumulative amount of mercury children are exposed to, but parents should not abandon vaccination as a means to do that.

Q8. If there are vaccines that are mercury-free, why shouldn't I just ask for those?

A. The American Academy of Pediatrics, the Advisory Committee on Immunization Practices for CDC and the Surgeon General all recommend that parents do not let their child miss a vaccination when safe and effective vaccines are available. Today, we are discussing a minimal, if any, risk from cumulative levels of mercury from some vaccines versus the large and devastating risk of childhood diseases like bacterial meningitis and whooping cough if parents and physicians abandon vaccination during this transition period. The American Academy of Pediatrics, the Advisory Committee on Immunization Practices for CDC and the U.S. Surgeon General want parents to be fully informed about children’s vaccines and if you have questions or concerns, we encourage you to speak to your child’s trusted health care provider.

Q9. I’ve heard that children may be getting toxic levels of mercury from vaccines. Is that true?

A. Everyone is exposed to mercury, even in some foods and household products. As part of an ongoing assessment of mercury in the environment and in products, many agencies have developed guidelines for acceptable levels of mercury--levels many times below any amount known to cause harm. Some children, depending on which vaccines they receive and the timing of those vaccines, are exposed to cumulative levels of mercury close to the safety ranges of guidelines. To further increase this margin of safety, clinicians and parents can take advantage of the flexibility within the existing immunization schedule. It’s important to understand that these highest acceptable levels include a “safety cushion” to take into account all the variables that people face in their exposures to mercury. No children are getting toxic levels of mercury from vaccines.

Q10. Are there vaccines available to prevent childhood diseases without exposing them to mercury?

A. Yes, although you may discover that these vaccines are not immediately available from your health care provider. The American Academy of Pediatrics, the Advisory Committee on Immunization Practices for CDC and the Surgeon General all recommend that parents do not let their child miss a vaccination when safe and effective vaccines are available. Today, we have a minimal, if any, risk from minute levels of mercury-containing thimerosal in some vaccines versus the large and devastating risk of childhood diseases like bacterial meningitis and whooping cough if parents and physicians abandon vaccination during this transition period. The American Academy of Pediatrics, the Advisory Committee on Immunization Practices for CDC and the U.S. Surgeon General want parents to be fully informed about children’s vaccines and if you have questions or concerns, we encourage you to speak to your child’s trusted health care provider.

Q11. Why is the Public Health Service and AAP making these recommendations now?

A. Although mercury is found in the environment, in food and in household products, exposure to mercury is of concern and, when possible, should be avoided. The Public Health Service agencies, the American Academy of Pediatrics, and vaccine manufacturers agree that thimerosal should be reduced or eliminated in vaccines. Some children, depending on which vaccines they receive and the timing of those vaccines, are exposed to cumulative levels of mercury close to the safety ranges of guidelines. The mercury levels being discussed are within the safety margins; however, we are working toward further increasing the margin of safety that already exists. It is important that we limit the cumulative amount of mercury children are exposed to, but parents should not abandon vaccination as a means to do that.

Q12. Why are chemicals and other substances added to vaccines?

A. Many things in today's world, including foods and medicines, have chemicals added to them to prevent the growth of germs and reduce spoilage. Chemicals are added to vaccines for similar reasons, to inactivate a virus or bacteria and to stabilize it, helping to preserve the vaccine and prevent it from losing its potency over time.

Some additives are used in the production of vaccines. Vaccines may include suspending fluid (e.g., sterile water, saline, or fluids containing protein); preservatives and stabilizers (e.g., albumin, phenols, and glycine); and adjuvants or enhancers that help the vaccine improve its immunogenicity (ability to protect against disease).

Q13. I understand some people are sensitive to thimerosal and must avoid it. Do they have problems with thimerosal-containing vaccines?

A. Most patients do not develop reactions to thimerosal given as a component of vaccines even when they’ve had a patch or intradermal tests for thimerosal that indicated hypersensitivity. Hypersensitivity to thimerosal usually consists of local, delayed reactions.

Q14. How can I find out what chemical additives are in specific vaccines?

A. Ask your health care provider or pharmacist for a copy of the vaccine package insert. The package insert lists ingredients in the vaccine and discusses any known adverse reactions.

Q15. What is mercury?

A. Mercury is a chemical element. As such it is neither created nor destroyed -- the same amount of mercury has existed since the earth was formed. Mercury is toxic to humans and wildlife. Organic forms of mercury are the forms of mercury to which humans and wildlife are generally exposed, usually from eating fish which have accumulated mercury in their muscle tissue. Uses and releases of mercury have been reduced very substantially in recent decades in the U.S. and most other industrialized countries.

Q16. Who is most vulnerable to mercury?

A: Two groups are most vulnerable to methyl mercury: the fetus and children ages 14 and younger. Children may be at higher risk of mercury exposure than are adults because they eat more per pound of body weight and because they may be inherently more sensitive than adults since their nervous systems are still developing.

Q17. Which population groups have the highest levels of mercury?

A: Groups that tend to have higher exposure include subsistence and frequent recreational fishers, people of Asian origin, and some Native American groups. The typical U.S. consumer eating fish from restaurants and grocery stores are not in danger of consuming harmful levels of mercury from fish and are not advised to limit fish consumption. Everyone is exposed to mercury, even in some foods and household products.

Q18. How can parents learn more about children’s immunizations?

To learn more about children's immunizations, vaccinations, or baby shots from a CDC information specialist, please call CDC’s National Immunization Information Hotline: 1-800-232-2522, for English, 1-800-232-0233, for Spanish.


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