Thimerosal is an ethyl mercury that is suspected of causing neurological damage-possibly resulting in ADHD and learning problems-and has been banned from all vaccines in the UK, the US and other developed countries for around 10 years. At the time the influential American Academy of Pediatrics (AAP) recommended its removal, and the United Nations is campaigning to have it banned from all vaccines supplied worldwide.
But the UN's efforts suffered a serious blow this week when the AAP came out in favour of supplying thimerosal-based vaccines to the developing world. Why the sudden change? According to the AAP, it claims it was too hasty in condemning thimerosal back in 1999, and there is no good evidence that it causes any harm to our children.
But there's another reason: thimerosal keeps production costs down because the vaccines can then be produced in multi-dose vials. Without this, production costs would increase five-fold.
Despite assurances of safety, don't expect to see thimerosal in vaccines for the developed world any time soon.
(Source: Pediatrics, 2012; doi: 10.1542/peds.2012-1760).