It is not. The mercury in (some, but not all or even most, these days) vaccines is ethyl mercury. Here is an article that explains a bit more of the similarity with dimethyl mercury, though - they are both organic mercurials:
>Both ethyl mercury and Hg2+ are very neuro toxic compounds. However, ethyl mercury is more rapidly partitioned into the hydrophobic (fatty) tissues of the central nervous system and is a more potent neuro toxin than Hg2+ based on this “partitioning factor”. It is this partitioning factor that makes organic mercurials such as dimethyl mercury so neuro toxically lethal (this is the compound that caused the death of a Dartmouth University chemistry professor after she was exposed to a drop or two on her gloved hand).
>The concern with organic mercurials, such as thimerosal, is that such compounds can be perceived as “pro toxicants” just as certain pharmaceuticals can be classified as “pro drugs”. This means that the original compound, e.g. thimerosal, is less reactive giving the compound time to partition into certain areas of the body before it breaks down releasing the ethyl mercury and then further releasing Hg2+. However, while attaching ethyl mercury to thiolsalicylate makes the ethyl mercury less reactive it most likely allows increased partitioning into the central nervous system before the ethyl mercury is released and thereby, increases the neuro toxicity per unit ethyl mercury involved
It took a year to die from 4mg of dimethyl mercury. If it took that long to die from injection with an excess of ethyl mercury, would we even find out why they died?
My comment was about how it was obviously not dimethyl mercury.
Whether or not we would detect some hypothetical unspecified toxic effect caused by some other substance would presumably depend on the nature of the effect and how prevalent it is.
