A big concern among parents seems to be preservatives used in vaccines, especially mercury-containing thimerosal. This study was a short one that looked at different preservatives and their effect on the immunity-producing components of bacteria.
Often it is desirable to separate out just the part of a pathogen that an immune response targets best and make a vaccine out of that, because that way you get a good, focused immune response against the important part and don't have anything else that could produce unwanted reactions. So Krueger and Nichols had developed a method to purify bacterial antigens, removing all whole bacterial cells from them, resulting in a product called Undenatured Bacteria Antigen, or UBA.
Using preservatives in vaccine preparations was often a good idea, because a bacterial contamination could lead to pretty bad outcomes in the recipients who received vaccines by injection. So this study tested how harsh different preservative candidates were on the UBA.
The ones they tested were tricresol, phenol, and merthiolate (aka thimerosal or thiomersal). The concentrations they used of the first two were much higher than of the third, more than 10 times higher, presumably because they didn't inhibit bacterial growth very well at lower concentrations. But they tried three different concentrations of merthiolate, going as low as 20 parts per million, or 0.002%. Then they tested how much UBA was denatured over time.
Denaturation by all of them was as complete as it was going to be by one week, and didn't increase beyond that. UBA with no preservative remained mostly undenatured, 95%, while that with phenol or tricresol was nearly half denatured. Merthiolate was intermediate, the lower concentration the better, between 24 and 37% denaturation.
So it seemed that merthiolate was the best preservative to use for preserving UBA.
Citation: Krueger, A. P. & Nichols, V. C. Effect of Preservatives on Undenatured Bacterial Antigens. Exp Biol Med 34, 335–337 (1936).
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