As with all medicinal products, vaccine safety is continually monitored by the Medicines and Healthcare products Regulatory Agency (MHRA) and its independent expert advisory body, the Committee on Safety of Medicines (CSM).
The only vaccines currently used in the routine childhood immunisation programme that contain thiomersal (also known as thimerosal) are the combined diphtheria/tetanus/wholecell pertussis/Haemophilus influenzae type B and the diphtheria/tetanus vaccines. Measles/mumps/rubella (MMR) vaccine does not contain thiomersal.
The MHRA and CSM have thoroughly reviewed the safety of thiomersal-containing vaccines, including alleged links with autism, on a number of occasions. In 2001, CSM conducted a major review of the available evidence and has considered new data as it has emerged. Following a review of further studies in 2003, including two United Kingdom studies involving more than 100,000 children, CSM advice was placed on the MHRA website at http://medicines.mhra.gov.uk. Further studies from Denmark involving almost half a million children have also specifically investigated the suggested link between thiomersal-containing vaccines and autism. None of these studies found any evidence of a causal association.
On the basis of the available data, the advice of CSM remains that there is no evidence of harm from thiomersal contained in vaccines, with the exception of possible hypersensitivity reactions (typically skin rashes or local swelling at the site of injection). The CSM advises that the benefits of immunisation with such vaccines outweigh any potential risks of vaccination. This view concurs with that of the World Health Organisation.