geni said:
There is only one vaccine (oneof the flu ones) commonly adminstered to infants in the US that contains thimerosal. Anything that has been used as a preservative in vaccines has upset the anti vac brigade.
Thanks for the info Geni. I'd ask you why the anti-vac brigade doesn't like the alternative preservatives except I'm not particularly interested in their opinion on anything…
I also found more info on line -- hopefully others will find it of interest also. These links are not for scientists like the one you posted (it was great, and hopefully one day I will fully understand it

), but for non-scientists.
The next two links state that single-dose vials don’t require preservatives but that multi-dose vials do.
Source
Consistent with this goal, FDA has encouraged and worked with manufacturers to develop new vaccines and new vaccine formulations that are either thimerosal-free or contain only trace amounts of thimerosal. The substantial elimination of thimerosal from pediatric as well as other vaccines has been achieved because over time, it has been possible to replace multi-dose vials with single-dose presentations (vials or syringes), which do not require a preservative.
Source
Manufactures can make vaccines free of mercury preservative simply by changing from multi-dose vials to single-dose vials, which do not need a preservative.
The last link explains:
*The difference between a single and multi-dose vaccine.
* Confirms that thimerosal is added to flu vaccines because typically it is only available in a multi-dose vial.
* Pharmaceutical companies are working on alternatives to thimerosal; so far, alternative stabilizers have made the vaccines less effective.
Source
What the difference between a single dose and a multi-dose vaccine?
A single dose vaccine is one that is stored in a single vial that is disposed of after the one doseis given to a person. With a multi-dose vaccine, multiple vaccine doses are stored in a singlevial and the doses from the same vial are given to different people.
…
Why is thimerosal used in the flu vaccine if other vaccines do not contain it?
The flu vaccine is generally marketed in a multi-dose vial and thimerosal is added to the manufacturing process to maintain sterility of the vaccine. Thimerosal also has a stabilizing
effect in the vaccines, ensuring that they are effective.
The flu vaccine contains thimerosal as a preservative, but, for the 2005/2006 season,
manufacturers are developing a thimerosal-free, stable, vaccine available for children.
Thimerosal will continue to be used in multi-dose vaccines until a safe alternative is found.
Could another preservative be used in multi-does vaccines like the flu vaccine?
Yes. Pharmaceutical companies are actively working on alternatives to thimerosal as a
preservative. If alternatives are used, they will need to be tested in clinical trials to evaluate their safety and effectiveness as preservatives. In some initial tests, alternative stabilizers have
actually made the vaccines less effective.
Emphasis added.
FWIW, my guess is that:
* Single dose vaccines can be sealed in a way that precludes the need for preservatives.
* It is less expensive to manufacture, distribute and store multi-dose vaccines than single-dose vaccines.