Thimerosal and Vaccines
Thimerosal and Vaccines
Abstract & Commentary
Synopsis: Thimerosal is a mercury-containing additive that has been included in many vaccine preparations because of its antibacterial effects. Recent concern about mercury poisoning has prompted an effort to develop effective vaccines that do not contain thimerosal and to avoid the unnecessary use of thimerosal-containing vaccines in young children.
Sources: Thimerosal in vaccines: A joint statement of the American Academy of Pediatrics and the Public Health Service. MMWR Morb Mortal Wkly Rep 1999;48(26):563-565; Pediatrics 1999;104:568-569.
In 1997, the food and drug administration (fda) of the United States was charged with reviewing and assessing the risk of all food and drugs containing mercury. This led to concern about the use of thimerosal, a mercury-containing preservative used in vaccines for decades. There is no evidence that any child has been seriously harmed by thimerosal, but efforts are under way to remove the theoretical risk of thimerosal toxicity, especially for young children.
Planned actions include a request for manufacturers to eliminate or reduce the mercury content of their vaccines, an expedited FDA review of new thimerosal-free vaccines, and further studies about the effect of these efforts on vaccine risk and benefit. It is still recommended that children be immunized as previously recommended by the CDC and the American Academy of Pediatrics. The risks of not vaccinating children far outweigh the unknown and much smaller risk of exposure to thimerosal-containing vaccines.
Comment by Philip R. Fischer, MD, dtm&h
Thimerosal (sodium ethylmercurythiolate) is a component of several vaccines that are commonly used by travel medicine practitioners for both routine and pre-travel immunization. This mercury-containing additive has several effects1 but is particularly useful as an antibacterial agent in preserving vaccines, especially those in multiple-dose preparations. The thimerosal status of some US-licensed vaccines is listed by "generic" and brand name in the accompanying Table.
| Table-Thimerosal and Vaccines2,5 | |
| Vaccine ` | Contains Thimerosal? |
| DTaP | |
| Acel-Imune | Yes |
| Tripedia | Yes |
| Certiva | Yes |
| Infanrix | No |
| DTP, TD, Td | Yes |
| DTP-Hib (Tetramune) | Yes |
| DTaP-Hib (TriHIBit) | Yes |
| Hib | |
| HibTITER (multidose) | Yes |
| HibTITER (single dose) | No |
| ActHIB, Omni HIB, PedvaxHIB | No |
| PROHIBit | Yes |
| Hib-HepB (COMVAX) | No |
| HepB (Recombivax HB, old formulation) | Yes |
| HepB (Recombivax HB, new formulation) | No |
| HepB (Engerix-B, old formulation) | Yes |
| HepB (Engerix-B, pending new formulation) | No |
| HepA | No |
| IPV | No |
| Influenza | Yes |
| JEV | Yes |
| Lyme | No |
| MMR | No |
| Meningococcal | Yes |
| Pneumococcal | |
| Pnu-Imune 23 | Yes |
| Pneumovax 23 | No |
| Rabies | |
| Rabies Vaccine Adsorbed (Bioport) | Yes |
| IMOVAX | No |
| Rabavert | No |
| Typhoid | No |
| Varicella | No |
| Yellow Fever | No |
So, what is the risk of using thimerosal-containing vaccines? First, it should be emphasized that the risk of mercury toxicity from routine vaccination is only hypothetical. Millions of children, even small newborn babies, have received thimerosal in their vaccines without adverse effect. To my knowledge, there are no reports of mercury poisoning resulting from routine vaccination. Second, there are some mercury-sensitive atopic children who have exacerbations of their atopic dermatitis following receipt of thimerosal-containing vaccines. Dermatitis, however, does not need to hinder the regular completion of routine vaccination.3
What should clinicians do? First, we must continue to vaccinate children and travelers. The risk of vaccine-preventable illnesses greatly outweighs the risk of mercury toxicity from thimerosal. The CDC has already expressed concern that misinterpretation of recent suggestions is leaving hundreds of American children at high risk of developing hepatitis B infections.4,5 Second, when equally effective thimerosal-free vaccines are available (as is the case for DTaP, Haemophilus influenza type b, and pneumococcal vaccines), practitioners might selectively purchase and use the safer alternatives. Third, while awaiting local availability of thimerosal-free vaccines, the timing of routine immunization might be delayed slightly in small babies as long as it still fits within the routine schedule’s planned time ranges. This might happen when waiting on the first hepatitis B vaccination for a baby born to a HBsAg-negative mother until two months of age, when a thimerosal-free vaccine may be used. However, since most travelers present just before their intended departure, travel medicine practitioners will rarely choose to delay needed vaccination. The dose of mercury in thimerosal-containing vaccines makes these concerns even less important in older children and adults. Fourth, we can be grateful for the preemptive, proactive, precautionary action being taken by the FDA and the CDC as they seek to reduce the already low risk of mercury toxicity. COLOR=black>
References
1. Elferink JG. Gen Pharmacol 1999;33:1-6.
2. American Academy of Pediatrics. Pediatrics 1999; 104:570-574.
3. Patrizi A, et al. Contact Dermatitis 1999;40:94-97.
4. Tucker ME. Pediatric News 1999;33:1&4.
5. MMWR Morb Mortal Wkly Rep 1999;48:996-998.
Thimerosal-containing vaccines:
a. have been linked to mercury poisoning in children.
b. should no longer be used.
c. are safe and effective in preventing many life-threatening diseases.
d. should never be replaced.
e. will add to the expense of vaccine manufacture over the next five years.
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