Other than minor responses such as redness and swelling at the injection site for one to two days, there is no evidence that the amount of mercury in vaccines causes harm, according to Centers for Disease Control and Prevention. With the exception of some flu vaccines, the mercury-based additive thimerosal has not been used in vaccines since 2001. For a short time thereafter, some vaccines still had trace amounts of thimerosal due to residue from the manufacturing process.
Shortly after entering the body, thimerosal turns into ethylmercury and thiosalicylate, two substances that are easily disposed of in a person's body, states the CDC. Since the mercury additive does not stay in the body for long, it is unable to accumulate and reach harmful levels. Found in certain types of fish but not in vaccines, methylmercury can be toxic since it does stay in the body for a longer time.
Many well-regarded studies have determined that the levels of exposure to mercury in vaccines does not correlate to an increase of autism, the CDC explains. To the contrary, the rate of autism has continued to escalate since the removal of thimerosal. The measles, mumps and rubella vaccine, as well as the varicella, pneumococcal conjugate and inactivated polio vaccines have never contained thimerosal.