27-Jan-03: Mercury (thiomersal) and Vaccines Statement: 16/01/03

No Thiomersal in MMR

Ethylmercury is present in some vaccines in a compound called thiomersal. It is used in some vaccines to keep the vaccine free of contamination. It has been used in vaccines for over 60 years and has played an important role in maintaining vaccine safety. There is no thiomersal in MMR.

The Committee on Safety of Medicines (CSM) has examined the link between thiomersal and neurotoxicity. The CSM advised that there is no evidence of harm caused by doses of thiomersal in vaccines, except for hypersensitivity reactions (such as allergic skin reactions). There is no evidence of a link between hypersensitivity reactions and the development of autism.

Two new studies have been completed (one funded by DoH, and the other by WHO) in the UK. They looked at a possible link between mercury in vaccines and neurodevelopmental disorders in children. Neither of the studies, involving over a hundred thousand children, finds a link between thiomersal exposure and neurodevelopment disorders, including autism.

A further study, published recently in the medical journal ‘The Lancet’, found that ethylmercury is very rapidly eliminated from babies’ bodies and did not accumulate. The paper found that the level of mercury in blood was no higher in children after vaccination than at birth. Claims of neurological damage have been based on toxicity from methyl mercury, not present in thiomersal.

Background

1. Thiomersal has been used in vaccines for over 60 years. It has played an important role either as a preservative to prevent microbial contamination or as an inactivating agent to produce killed vaccines.
2. Thiomersal is present in the final product of the following routine childhood vaccines: DTwP (and DTwP/Hib) and Td. It is also used in DT. It is not used in MMR, Men C, Hib polio or BCG.
3. The mercury content of thiomersal has given rise to theoretical concerns of possible neurotoxic effects. Mercury is neurotoxic in high doses and there has been speculation that mercury exposure from thiomersal could lead to autism, or other developmental problems in children. However, no neurotoxicity has been demonstrated as a result of the low level of thiomersal exposure from routine vaccination.
4. In September 2001, the Committee on Safety of Medicines (CSM) reviewed the currently available data relating to possible neurotoxicity of thiomersal in vaccines and advised that there is no evidence of harm caused by doses of thiomersal in vaccines, except for hypersensitivity reactions.
5. Hypersensitivity reactions (such as allergic skin reactions) are the only identified harmful effects of thiomersal contained in vaccines. Serious allergic reactions are rare. The available evidence does not support a link between thiomersal in vaccines and autism or other neurological conditions. There is no evidence of a link between hypersensitivity reactions and the development of autism.
6. We are aware of two new studies in the UK looking at the relationship between mercury in vaccines and neurodevelopmental disorders in children. One of these studies is funded by the Department of Health and used the Avon Longitudinal Study of Pregnancy and Childhood. The other study used the General Practice Research Database and is funded jointly by the World Health Organisation and the Public Health Laboratory Service (which receives its funding from the Department of Health). Neither of these studies support an association between thiomersal exposure through the UK programme and neurodevelopmental disorders (including autism) in children.
7. A study by M Pichichero et al describing the elimination of mercury from the body following administration of thiomersal-containing vaccines was published in The Lancet in November 2002. The results of this study show that giving thiomersal-containing vaccines does not raise blood levels of mercury and that ethylmercury (from thiomersal) is rapidly eliminated from blood via the faeces after vaccine administration. In a letter accompanying the article, it is stated that ‘this study gives comforting reassurance about the safety of ethylmercury as a preservative in childhood vaccines’.
8. Because thiomersal contains mercury, both the European Medicines Evaluation Agency and the Food and Drug Administration in the United States have recently recommended that vaccine manufacturers phase out its use wherever possible purely as a precaution. Experts advise that the benefits of vaccination far outweigh the risks, if any, of exposure to thiomersal containing vaccines. Manufacturers are actively developing research programmes to eliminate, substitute or reduce thiomersal in vaccines, following the European recommendations. This may take time because manufacturers are required to ensure that the replacement or elimination of thiomersal does not affect the safety, quality and efficacy of the final vaccine.
9. There is a DTaP vaccine (diphtheria/tetanus/acellular pertussis vaccine) licensed in the UK that does not contain thiomersal. This is not routinely offered as part of the primary immunisation schedule because this vaccine is not as effective in protecting against pertussis as DTwP. The benefits of DTwP outweigh any risks, if any, from the thiomersal present in the vaccine.

Back to MMR news