The answer is Yes: Thimerosal 0.01% (sodium ethylmercurithiosalicylate) is an ingredient in the Flu vaccine
Why is Thimerosal used a preservative in some vaccines?
Thimerosal is used as a preservative in some multi-dose vials of vaccines to prevent contamination. Preservatives are not required for vaccines in single-dose vials. As a preservative, thimerosal is added at the end of the production process to the bulk or final container to prevent contamination after multi-dose vials are opened.
It has been used since the 1930s, but Canadian and U.S. health officials have removed it from most childhood vaccines. Today, according to the U.S. Food and Drug Administration, the only vaccines routinely recommended for children 6 years of age and younger that contain thimerosal are: one vaccine for DTaP, and three vaccines for influenza (flu). These four vaccines contain trace amounts of thimerosal --0.5 micrograms of mercury per dose, that is, a given dose of vaccine contains less than 1 part per million. Two hepatitis B vaccines, four Hib vaccines, and two DTaP vaccines are thimerosal-free.
Prior to the recent initiative to reduce or eliminate thimerosal from childhood vaccines, the maximum cumulative exposure to mercury via routine childhood vaccinations during the first six months of life was 187.5 micrograms. With the newly formulated vaccines, the maximum cumulative exposure during the first six months of life will now be less than three micrograms of mercury; this represents a greater than 98% reduction in the amount of mercury a child would receive from vaccines in the first six months of life. Influenza (flu) vaccine is not given until six months or older.
In the body, thimerosal is metabolized or degraded to ethylmercury. Luckily, ethylmercury has not been found to bioaccumulate (bioaccumulation refers to the accumulation of substances, such as pesticides, or other organic chemicals in an organism. Bioaccumulation occurs when an organism absorbs a toxic substance at a rate greater than that at which the substance is lost. Thus, the longer the biological half-life of the substance the greater the risk of chronic poisoning, even if environmental levels of the toxin are not very high).
The toxicity of ethylmercury is not well studied, but exposure standards based on methylmercury are not demonstrated to be equivalent for ethylmercury. Methylmercury is a bioaccumulative environmental toxicant.
Ingested methylmercury is readily and completely absorbed by the gastrointestinal tract. It is mostly found complexed with free cysteine and with proteins and peptides containing that amino acid. The methylmercuric-cysteinyl complex is recognized by amino acid transporting proteins in the body as methionine, another essential amino acid. Because of this mimicry, it is transported freely throughout the body including across the blood-brain barrier and across the placenta, where it is absorbed by the developing fetus. Also for this reason as well as its strong binding to proteins, methylmercury is not readily eliminated. Methylmercury has a half-life in human blood of about 50 days.
Obviously, more long term studies are needed to fully understand the effects of this preservative. I checked the CDC's website to get more information: The National Institute of Allergy and Infectious Diseases (NIAID) at the National Institutes of Health (NIH) funds thimerosal research that focuses on better understanding of what happens to thimerosal once it is introduced into the body and how this compares to current knowledge of methyl mercury pathways.
Taken from the CDC's website: A recent study sponsored by the NIAID and conducted at the University of Rochester assessed mercury levels in 40 infants who received vaccines containing thimerosal and 21 infants who received thimerosal-free vaccines. The scientists measured the level of mercury in the infants' blood, urine, and stool up to 28 days after vaccination.
They found: infants who were given vaccines with thimerosal had levels of mercury well below the safe level of 29 nmol/L (this level is set ten times lower than the level at which mercury begins to cause neurological problems); and the body seems to be able to get rid of thimerosal (ethylmercury) via the gastrointestinal tract (stools) much quicker than it gets rid of methylmercury. For more information about the different types of mercury, visit Frequently Asked Questions about Mercury and Thimerosal.
NIAID and the National Institutes of Environmental Health Sciences (NIEHS) are also funding studies comparing the pharmacokinetics and tissue distribution of thimerosal, ethylmercury, and methylmercury in non-human primates. Pharmacokinetics is the study of how an agent is absorbed, distributed, metabolized (broken down), and excreted. For more information, visit NIAID Research on Thimerosal. The Food and Drug Administration (FDA) has been actively addressing the issue of thimerosal as a preservative in vaccines. For information, visit Thimerosal in Vaccines.
CDC's Center for Environmental Health and the National Center for Health Statistics are doing a study looking at all mercury exposures and working with the National Health and Nutrition Examination Survey (NHANES). NHANES 4 will collect samples of blood, hair, and urine from all women of reproductive age and children under 5 to assess mercury levels in the body from all sources of mercury a person can be exposed to in the environment. Findings of a study conducted using NHANES 3 data to check blood and hair mercury levels suggest that the mercury levels in young children and in women of childbearing age are generally below the level considered hazardous (MMWR 50, 140–143).