Thimerosal Hype or Hazard

You know the story about vaccines and thimerosal, right?

Are you sure?

Thimerosal Timeline

Although it was never actually linked to any significant side effects, as a “precautionary measure,” the AAP recommended that thimerosal (mercury) be removed from childhood vaccines in 1999.

That’s not when the hype over thimerosal started though.

A few years before that, in 1997, an amendment to the Food and Drug Administration (FDA) Modernization Act called on the FDA to compile a list of foods and drugs with added mercury.

“At the time the FDA Modernization Act was passed, it was recommended that infants receive 3 different vaccines that contained thimerosal: diphtheria-tetanus-acellular pertussis (DTaP), hepatitis B, and Haemophilus influenzae type B (Hib). Infants who received all of these vaccines could have been exposed to a cumulative dose of mercury as high as 187.5 μg by 6 months of age. This value exceeded guidelines recommended by the Environmental Protection Agency (EPA) but did not exceed those recommended by the Agency for Toxic Substances Disease Registry (ATSDR) or the FDA.”

Offit et al on Addressing Parents’ Concerns: Do Vaccines Contain Harmful Preservatives, Adjuvants, Additives, or Residuals?

And it was found that in some circumstances, infants could get 187.5 μg of mercury from vaccines by 6 months of age, which exceeded some, but not all regulatory guidelines.

Which regulatory guidelines?

• EPA – 89 µg
• ATSDR – 266 µg
• FDA – 354 µg

That led to the recommendation from the AAP, in July 1999, to remove thimerosal from vaccines, including the hepatitis B, DTaP, and Hib vaccines, the only routinely used, non-flu vaccines that had ever had thimerosal. Specifically, the AAP asked vaccine manufacturers “for a clear commitment and a plan to eliminate or reduce as expeditiously as possible the mercury content of their vaccines.”

“There is a significant safety margin incorporated into all the acceptable mercury exposure limits. Furthermore, there are no data or evidence of any harm caused by the level of exposure that some children may have encountered in following the existing immunization schedule. Infants and children who have received thimerosal-containing vaccines do not need to be tested for mercury exposure.”

Notice to Readers: Thimerosal in Vaccines: A Joint Statement of the American Academy of Pediatrics and the Public Health Service

It is important to note that thimerosal-free versions of the DTaP and Hib were already available at the time though.

So we had:

• DTP vaccines – contained 25μg thimerosal, but had largely been replaced by DTaP vaccines at this point
• Infanrix – a DTaP vaccine that never contained thimerosal since it was first approved in 1997 (most folks incorrectly state that Infanrix first contained trace amounts of thimerosal)
• Tripedia – a DTaP vaccine that was first approved in 1992 and did contain 25μg thimerosal, a thimerosal-free formulation became available in March 2001 – it was discontinued in 2011
• Acel-Imune – a DTaP vaccine that was approved in 1991 and did contain 25μg thimerosal, it was discontinued in 2001
• Certiva – a DTaP vaccine that was approved in 1998 and did contain 25μg thimerosal, it was discontinued in 2000
• TriHIBit – a DTaP/Hib combination vaccine that was approved in 1997 and did contain 25μg thimerosal, it was discontinued in 2011
• Tetramune – a DTP/Hib combination vaccine that was approved in 19 and did contain 25μg thimerosal, it was later discontinued
• OmniHib – a Hib vaccine that never contained thimerosal since it was approved in 1993
• ActHIB – a Hib vaccine that never contained thimerosal since it was approved in 1993
• ProHIBIT – the first Hib conjugate vaccine licensed in 1987, it contained 25μg thimerosal
• PedvaxHIB – a Hib vaccine that never contained thimerosal since it was approved in 1989
• HibTITER – a Hib vaccine that never contained thimerosal since it was approved in 1988, except in multidose vials (25μg thimerosal)
• Comvax – a Hib/hepatitis B combination vaccine that never contained thimerosal
• Recombivax HB – a hepatitis B vaccine  with 12.5μg  thimerosal that was approved in September 1983, but a thimerosal-free formulation became available in September 1999
• Engerix B – a hepatitis B vaccine with 12.5μg  thimerosal that was approved in 1989, but a form with only a trace amount of thimerosal became available in March 2000, followed by a thimerosal-free formulation in January 2007

And of course, the other vaccines that younger kids got at the time never contained thimerosal, including hepatitis A, MMR, Varivax, polio, and Prevnar.

By January 2003, remaining stocks of vaccines with thimerosal expired.

Also in 2003, thimerosal-free flu vaccines became available, including thimerosal-free flu shots and FluMist, the nasal spray flu vaccine.

Thimerosal Hype or Hazard

So what was the big concern about thimerosal?

It wasn’t that infants were getting exposed to thimerosal in vaccines, but rather that they might get exposed to too much thimerosal.

Looking back at the available vaccines at the time, it is fairly obvious that most infants didn’t get that much thimerosal though, as there were already plenty of thimerosal-free versions of all routinely used vaccines. To get to the higher doses that some folks were concerned about, they would have to get the hepatitis B vaccine, plus thimerosal containing versions of both DTaP and Hib, and a flu shot.

Because young, otherwise healthy children are at increased risk for influenza-related hospitalization, influenza vaccination of healthy children aged 6-23 months is recommended.

Also, keep in mind that it wasn’t until 1991 that hepatitis B and Hib vaccines were added to the immunization schedule to be given to all infants.

And many kids didn’t get flu shots yet.

Remember, it was until the 2004-05 flu season that we started to see strong recommendations to give flu shots to anyone who wasn’t at high risk for complications from the flu. And by that time, thimerosal free flu shots were beginning to appear.

Still, the most important takeaway from all of this is that even though thimerosal was removed from vaccines, it was done as a precautionary measure and not because these kids were harmed. In fact, some kids were harmed in the process, especially as some infants didn’t get their newborn hepatitis B vaccine and at least one went on to get a fatal hepatitis B infection.

What to Know About Vaccines and Thimerosal

Even at the height of the thimerosal scare, most vaccines didn’t contain thimerosal.

More on Vaccines and Thimerosal

• An interview with Robert Kennedy Jr. on vaccines
• Correcting Robert F. Kennedy Jr.’s vaccine ‘facts’
• Addressing Parents’ Concerns: Do Vaccines Contain Harmful Preservatives, Adjuvants, Additives, or Residuals?
• Thimerosal and Vaccines — A Cautionary Tale
• Vaccine Ingredients – Thimerosal
• Thimerosal Fact or Fiction
• Thimerosal Fact Sheet
• MMWR – Notice to Readers: Thimerosal in Vaccines: A Joint Statement of the American Academy of Pediatrics and the Public Health Service
• CDC – Timeline: Thimerosal in Vaccines (1999-2010)
• CDC – Thimerosal in Vaccines
• CDC – Frequently Asked Questions about Thimerosal
• AAP – Thimerosal in Vaccines—An Interim Report to Clinicians
• FDA – Thimerosal and Vaccines
• CDC – Historical Reference of Seasonal Influenza Vaccine Doses Distributed
• CDC – Influenza vaccines — United States, 2017–18 influenza season
• IOM – Thimerosal-Containing Vaccines and Neurodevelopmental Disorders
• Study – Safety of Thimerosal-Containing Vaccines: A Two-Phased Study of Computerized Health Maintenance Organization Databases
• Thimerosal as a Preservative in Vaccines
• Mercury And Autism Not Linked, Again
• Prenatal Mercury and Autism
• Ask the Experts about Vaccine Safety
• Another Study Showing Lack of Correlation Between Mercury and Autism
• The Conspiracy-Ridden Worldview of Robert F. Kennedy Jr.
• Mr. Kennedy, if you know the science, why did you claim that the MMR vaccine contains mercury?
• Is The CDC Hiding Data About Mercury, Vaccines, And Autism?
• Robert F. Kennedy, Jr. and his World Mercury Project: Antivaccine, NOT “fiercely pro-vaccine”
• Robert Kennedy Jr.’s strange remarks on autism
• Mr. Kennedy, if you know the science, why did you claim that the MMR vaccine contains mercury?
• Salon retracts Robert Kennedy’s “Deadly Immunity”

Last Updated on June 3, 2018