Thimerosal in Vaccines

Although it was never actually linked to any real side effects, thimerosal (mercury) was removed from almost all childhood vaccines in 1999.

Thimerosal, a preservative, only remained in flu vaccines for a few years, but thimerosal free flu vaccines have been available since 2003.

That’s also the year that the remaining non-flu vaccines with thimerosal expired – January 2003.

And this year, at least “120 million doses of thimerosal-free or preservative-free influenza vaccine will be produced.” That means that over 75% of flu shots are thimerosal free, leaving only some multi-dose vials of flu shots to still have thimerosal, but making it easy to avoid if you want to.

Myth of Continued Exposure to Mercury in Vaccines

Although most anti-vaccine groups have moved on to other conspiracy theories to scare parents, some still falsely claim that vaccines continue to be made with thimerosal and that thimerosal is dangerous.

Robert F. Kennedy Jr., for example, continues to claim that even though thimerosal has been removed from pediatric vaccines, “thimerosal levels remain virtually unchanged.” This is mostly, he claims, because of flu shots with thimerosal. Also, when a pregnant woman gets a flu shot, Kennedy claims that the fetus gets a bolus of thimerosal “that’s about 800 times the amount of mercury the CDC recommends.”

First, it is important to remember that the original concerns about thimerosal were because children who received a complete set of thimerosal containing vaccines (only hepatitis B, DTaP, and Hib ever had thimerosal) could get up to 187.5 micrograms of ethyl mercury by the time they were six months old, which exceeded the EPA limits for methyl mercury ingestion (but was less than the FDA limits). They aren’t the same type of mercury though, and thimerosal free versions of DTaP and Hib were already available in the late 1990s, so many kids likely got less than 187.5 micrograms of ethyl mercury.

Since thimerosal was removed from almost all vaccines beginning in 1999, that left flu vaccines as the main pediatric vaccine that still used thimerosal as a preservative. So did expanded flu shot recommendations for kids mean that they still got a lot of thimerosal over the years?

It is extremely unlikely that many kids have gotten each and every one of their yearly flu vaccines with thimerosal. It is more likely that they got just a few with thimerosal and the rest without, as thimerosal free flu vaccines became more widely available. After all, a flu vaccine with reduced thimerosal was available as early as 2002.

In 2003, thimerosal free flu shots became available and Flumist, a thimerosal free flu nasal spray vaccine was also approved. The supply of thimerosal free flu vaccines increased each and every year. For the 2014-15 flu season, over 100 million doses of flu vaccine are available that are thimerosal free or preservative free (with only trace amounts of thimerosal).

Even if kids did get flu vaccines with thimerosal each year though, would it matter? A 2008 study in Pediatrics, “Mercury Levels in Newborns and Infants After Receipt of Thimerosal-Containing Vaccines,” found that the half-life of ethyl mercury was about two days, “suggesting that exposure to thimerosal-containing vaccines does not result in an accumulation of mercury in blood.” And the highest blood level they found was less than 5-8 nanograms/ml, which is far less than the 187.5 micrograms that anti-vax groups continue to talk about, even in infants who had already received a cumulative dose of 162.5 micrograms of thimerosal.

What about flu shots in pregnancy?

A 2010 study in Pediatrics, “Prenatal and Infant Exposure to Thimerosal From Vaccines and Immunoglobulins and Risk of Autism,” found that “prenatal and early-life exposure to ethylmercury from thimerosal-containing vaccines and immunoglobulin preparations was not related to increased risk of” autism spectrum disorders. Two other studies have also found that prenatal exposure to thimerosal from immunoglobulin preparations, like Rho(D) immune globulin, during pregnancy were not associated with an increased risk for autism.

And also consider that fewer than 15 to 30% of pregnant women got flu shots before 2009. After 2009 and the H1N1 pandemic, rates did increase, but only to about 38 to 52%.

Although current recommendations don’t state a preference for the type of flu shot for pregnant women, it is likely that at least some of them got thimerosal free flu shots. In California, for example, since the passage of their Mercury Free Act in 2006, pregnant women and children younger than age 3 years have to get vaccines that are ‘mercury free.’

What To Know About Thimerosal in Vaccines

Thimerosal is a preservative that was removed from vaccines beginning in 1999, which means that most teens today got little or no exposure to thimerosal from vaccines.

More Information About Thimerosal in Vaccines:

• CDC – Thimerosal in Vaccines Thimerosal
• Thimerosal in Vaccines
• Vaccine Ingredients – Thimerosal
• Timeline: Thimerosal in Vaccines (1999-2010)
• Thimerosal
• FDA – Thimerosal in Vaccines Questions and Answers
• Thimerosal
• Thimerosal and Vaccines
• Thimerosal as a Preservative in Vaccines
• Thimerosal and Autism Studies
• Mercury in vaccines as a cause of autism and autism spectrum disorders (ASDs): A failed hypothesis
• Is The CDC Hiding Data About Mercury, Vaccines, And Autism?
• What? Removing thimerosal from vaccines caused the autism epidemic?
• No, the thimerosal in the flu vaccine does not explain why autism rates did not go down

Updated April 8, 2017