Fears rise over mercury

Is there really a link between a preservative used in vaccines and autism in childrenIf the fuss over the MMR vaccine wasn’t enough to worry parents, along comes another immunological scare. This time it centres on the DTP (diphtheria, tetanus and pertussis) vaccine.

The standard vaccine, which goes under the trade name Trivax, contains thimerosal, a preservative containing mercury that is also occasionally known as thiomersal or ethyl mercury. It prevents vaccines spoiling, as well as inactivating some bacteria used in the preparations. European guidelines have recommended that, even though there is no evidence that the ingredient has damaged infants, vaccines containing the preservative should be gradually phased out as a precautionary measure.

A Sunday newspaper has been waging a lengthy campaign to get the vaccine replaced by a mercury-free alternative, marketed as Infanrix. In an echo of the uncertainty surrounding MMR, one report said that there was a possible link between the vaccine and cases of autism and neurological disorders, and that the mercury-free vaccine was being denied to GPs around the country.

However, according to the Department of Health, the campaign is based on scant evidence. “Trivax is as safe as a vaccine can get,” says spokesman Robert Beasley. He adds that Infanrix is not as effective as Trivax, and that it is being recommended only when Trivax is unavailable.

“There is a recommendation (from European drug authorities) that there should be a move away from vaccines containing thiomersal, not that the current vaccines should be withdrawn,” says Beasley. “Thiomersal has been used in vaccines for 50 years — there is no concern about the current levels in vaccines.”

Beasley says that a completely new vaccine — more effective than Infanrix and mercury-free — is awaiting approval by the Medicines Control Agency and will, if appropriate, replace Trivax as the standard vaccine. Trivax is usually administered as a course of three 0.5ml injections at two, three and four months. Thimerosal accounts for 0.01 per cent of the vaccine by volume. It was reported last month that the World Health Organisation (WHO) was beginning its own investigation into the compound. Dr John Clements, medical officer in the WHO vaccines and biologicals division, told Pulse: “We are looking to confirm or refute the suggestion that mercury in thiomersal might be responsible for minor brain dysfunctions in infants who have received vaccines. At the moment we have no evidence to support this claim.”

However, the WHO has previously voiced support for thimerosal-containing vaccines, which it says have been used safely for 60 years, because of far greater risks of not vaccinating, especially in the developing world. Some parents in America are suing a dozen pharmaceutical companies for health problems allegedly caused by thimerosal.

The WHO started its investigation after American researchers noted that some vaccinated infants were receiving mercury intakes that exceeded recommended levels. However, the authorities have been quick to stress that no children have been exposed to toxic levels and that greater mercury levels are found in fish. Dr William Egan, from the Food and Drug Administration, testified to the US House of Representatives that “there are no convincing data or evidence of any harm caused by the low levels of thimerosal that some children may have encountered in following the existing immunisation schedule”.

The Centers for Disease Control and Prevention in Atlanta, Georgia, notes: “Other than the occurrence of local hypersensitivity reactions, no harmful effects have been reported from thimerosal at doses found in vaccines.”

Both organisations stress that the risk of disease far outweighs the risk of an adverse reaction to the vaccine, and would be far more devastating. Beasley says the levels of thimerosal are higher in American vaccines, and that the research findings would not apply here.