Thimerosal. It is a mercury-based preservative found in children’s vaccines. The jury is still out on whether or not the neurotoxin is responsible for the life-altering condition known as autism especially as its use seems to correlate with the astronomical jump in the developmental disorder in children.

Ingemar Berling/Pressens BildLogically mercury is probably not a good thing to put into a childhood vaccines, especially since there are alternatives. If a dose is delivered in a single vial, there is no need for a preservative. Thimerosol is largely used so that multi-doses can be put into one vial to preserve the vaccine between uses and prevent bacterial or fungal contamination. That also keeps costs down for the manufacturer who does not have to rely on refrigeration.

The issue is so unsettled that a United Nations Environment Program (UNEP) draft treaty bans the use of thimerosal in vaccines.

So what is going on with the leading medical organization that is charged with promoting children’s health?

The American Academy of Pediatrics (AAP) has just voted to leave the preservative in vaccines. Publishing a statement in the online journal, Pediatrics, the academy decided to back a World Health Organization (WHO) stand that came out of a unanimous decision made at an April meeting of the WHO’s Strategic Advisory Group of Experts (SAGE).

The “leave the thimerosol in” gang fears that global access to vaccines for tetanus, diphtheria, pertussis and hepatitis B vaccines could be restricted if they do not contain the preservative.

This is a sharp reversal from 1999 when the AAP and U.S. Public Health Service called for the removal of mercury from all vaccines. After all it’s been shown there is a cumulative effect from mercury in vaccines especially for infants who are all put on an immunization schedule. Studies have demonstrated neurotoxic conditions arising from methyl mercury and thimerosol contains the closely related ethyl mercury, which studies have failed to connect to autism, reports Reuters.

In 2004, the Institute of Medicine discounted the thimerosal-autism link. A CDC study reported the same thing in 2010. The AAP then reversed its decision, reports Medpage Today.

But the WHO says there is no alternative to using thimerosol and since studies have failed to find a link to autism, its removal could make vaccines unavailable in countries where children can die from diphtheria and tetanus. The cost of switching to a single-dose vial was cited in this decision as well as the waste and manufacturing cost.

As if there should be any safe threshold for mercury injected into an infant? When there is a doubt but still some suspicions, whose side do we want to err on?