Unsafe Thimerosal or Mercury in Vaccines?

Mercury in Vaccinations?

Mercury in vaccinations?

Thimerosal (or thiomersal) in vaccines is probably one of the most brought up things in a conversation with people who are concerned with vaccination. So at the start it’s good to clarify that in the United States (U.S.) and Europe vaccinations for infants 6 years old and under are thimerosal free (and hence mercury free).

In 1997 the FDA modernisation act called for a review and risk assessment of all food and drugs containing mercury and an extensive review was carried out on the thimerosal content of vaccines.1 Despite finding no evidence of harm from thimerosal it was decided to tell manufacturers to eliminate thimerosal from vaccines for infants under 6 years old as a precautionary measure. A joint statement from the U.S. Public Health Service, FDA, National Institutes of Health, CDC, HRSA and the American Academy of Pediatrics was issued to manufacturers in 1999 and then again in 2000.2 3 This set in motion the removal of thimerosal from vaccines.

All production of recommended infant vaccines containing thimerosal had stopped by 2002 and by 2003 all infant vaccines previously containing thimerosal would have passed their expiration date.4 That is to say, there are no infant vaccines left over in the system that still contain thimerosal.

What is thimerosal?

Thimerosal is an antiseptic and anti-fungal agent which means it kills bacteria and fungus. The thimerosal molecule contains a mercury atom and with the dangers of mercury exposure now common knowledge it’s hardly a surprise that parents were concerned on first hearing this. It was this mercury content that caused the FDA to evaluate and carry out a risk assessment on thimerosal in vaccines in compliance of the Act in 1997. Thimerosal was the only source of mercury in vaccines.

What infant vaccinations used to contain thimerosal in 1999?

Before thimerosal was removed from infant vaccinations in 1999 the assessment looked at thimerosal in vaccines for infants under 2 years old. The results are shown below:

Vaccine% Thimerosal concentration Amount of Mercury
(µg/0.5 mL)
Poliovirus (IPV and OPV)0NONE
Measles, mumps and rubella (MMR)0NONE
Diphtheria-tetanus-pertussis (DTP or DTaP).0125 µg/0.5 mL
Hepatitis B (HepB single antigen).00512.5 µg/0.5 mL
Haemophilus influenzae type b (Hib).0125 µg/0.5 mL
Influenza vaccine (only given to selected populations).00512.5 µg/0.5 mL

Table 1. Recommended vaccines for infants under 2 years old that contained thimerosal in 1999.5 6

This may raise some eyebrows because the perception some have is that all infant vaccinations used to contain thimerosal when in reality there were 3 and possibly the influenza vaccine if you were at risk. These contained 0.000025 grams of mercury in the form of thimerosal and some contained less as you can see in the table.

Why was thimerosal in those 4 infant vaccinations?

The Fluzone Influenza vaccine in its multi-dose vial contains a 0.01% concentration of Thimerosal to prevent contamination.

The Fluzone Influenza vaccine in its multi-dose vial contains a 0.01% concentration of thimerosal to prevent contamination. Courtesy of CDC/Jim Gathany

There are no prizes for guessing that it was added to vaccinations to prevent bacterial and fungal growth and there was a very good reason for this. In 1916 four children died and 60 others became severely ill in South Carolina after a typhoid vaccine became contaminated with bacteria (Staphylococcus aureus). Then another tragic incident struck in Australia in 1928, where Dr. Ewing George Thomson was vaccinating children against diphtheria. He opened the bottle containing the vaccine and proceeded to inject 21 children with no problems at all. The second round of vaccination took place some days after and of the 21 children he vaccinated, 12 died.7

Why? Simply because staphylococci bacteria had entered the bottle during the first round of vaccinations, multiplied in the solution and were at sufficient levels to kill when the next vaccinations took place. This was investigated by a Royal Commission who recommended that to prevent further deaths from contamination, the vaccine should contain an antiseptic to prevent bacterial growth or be issued in single use containers. In the 1940s thimerosal was chosen due to its effectiveness at very low levels in preventing bacterial growth and also because it did not interfere with the vaccine potency.8 Animal studies had also shown that levels many times higher than what were present in vaccines resulted in no negative effects.9 It was considered safe.

Why was thimerosal not in the other infant vaccinations?

The reason why these never contained thimerosal is because it would actually damage these vaccines making them ineffective. In order to give us immunity the viruses in these vaccines have been badly disabled or inactivated enough to prevent disease but still allow an immune response. However, thimerosal would completely destroy them preventing activation of our immune system and defeating the purpose of the vaccine in the first place. You’ll find that these vaccines come in single dose vials or syringes so that there can be no possibility of contamination as in vaccines that come in multi dose vials. It’s more expensive, but it’s the only safe way to do it.

The list of current vaccines recommended for infants under 6 years old

As we mentioned at the beginning, the recommended vaccines now given to children under 6 years old don’t contain thimerosal. So now that we’re in the year 2015 here is the choice of vaccines recommended in the U.S. for infants under 6 years old.

The influenza vaccinations do contain thimerosal if they are in multi-dose vials, however, single-dose options that don’t contain thimerosal are available if you are concerned. If you want to know more about any of the vaccines, simply click on the vaccine name. You’ll be taken to the FDA approval page for the vaccine that contains the vaccine product information, studies done and communication with the manufacture during the approval process.

Vaccines that use thimerosal in the manufacturing process but have it removed before the finished product still contain trace amounts.  The word ‘trace’ instead of ‘none’ is used to indicate this in the thimerosal status concentration column of the table. If the word ‘trace’ is not used then it was not present in the manufacturing process.

VaccineTrade name Thimerosal Status concentration (Mercury) 
Pneumococcal conjugatePrevnarNONE
Prevnar 13NONE
Inactivated PoliovirusIPOLNONE
Varicella (Chicken Pox)VarivaxNONE
Mumps, measles and rubellaM-M-R-IINONE
Mumps, measles, rubella and varicellaProQuadNONE
Hepatitis AHavrixNONE
Hepatitis BRecombivax HBNONE
Engerix BNONE
Haemophilus influenzae type b conjugate (Hib)ActHIBNONE
Hib/Hepatitis B combinationComvaxNONE
Seasonal Trivalent InfluenzaFluzone (multi-dose)0.01% (12.5 µg/0.25 mL dose, 25 µg/0.5 mL dose)
Fluzone (single-dose)NONE
Fluvirin (multi-dose)0.01% (25 µg/0.5 mL dose)
Fluvirin (single-dose)Trace (<1ug Hg/0.5mL dose)
Fluarix (single-dose)NONE
Afluria (multi-dose)0.01% (24.5 µg/0.5 mL dose)
Afluria (single-dose)NONE
Seasonal influenza liveFluMistNONE

Table 2. List of recommended vaccines for children under 6 years old, showing that only the influenza vaccine in its multi-dose format still contains thimerosal. Information current as of 2014. As always consult a doctor for the most recent information.10

Infant vaccines in the U.S. and Europe are thimerosal free

It’s plain to see that the vaccinations recommended for 6 years old and younger are thimerosal free (and hence mercury free), except for some influenza vaccinations but even they have thimerosal free options. I hope that this goes some way to putting your mind at ease regarding mercury content of vaccinations. As always if you have specific questions regarding a type of vaccination please contact your doctor for the most recent and reliable information or forward this article to them for their opinion.

Further Reading

Who decides the vaccination schedule?

A look at who decides our vaccination schedule and the role that pharmaceutical companies play in the vaccine process.

My name is David Hamilton and I’m from Northern Ireland but currently living in Puerto Rico. I have a degree in Biochemistry and a M.Phil in molecular virology from Queen’s University Belfast. I write on some of my interests which range from virology, astronomy and science related subjects to history. Thanks for your interest!


  1. U.S. Congress. 1997. Food and Drug Administration Modernization Act of 1997. Food and Drug Administration study of Mercury compounds in drugs and foods. Section 413.
  2. Notice to Readers: Thimerosal in Vaccines: A Joint Statement of the American Academy of Pediatrics and the Public Health Service. 1999
  3. Joint Statement Concerning Removal of Thimerosal from Vaccines. 2000
  4. Centers for Disease Control and Prevention. 2013. Understanding Thimerosal, Mercury, and Vaccine Safety.
  5. Ball L.K., Ball R. and Pratt R.D. 2001. An assessment of thimerosal use in childhood vaccines. Pediatrics. 107 5:1147-54.
  6. American Academy of Pediatrics. 1999. Thimerosal in vaccines – An interim report to clinicians. Pediatrics Vol. 104 No. 3
  7. Wilson G.S. 1967. The Hazards of Immunization. New York, NY: The Athlone Press; 75–84
  8. Jamieson W.A. and Powell H.M. 1931. Merthiolate as a Preservative for Biological Products. American Journal of Hygiene 14:218–224.
  9. Powell H. M. and Jamieson W.A. 1931. Merthiolate as a Germicide. American Journal of Hygiene 13: 296–310.
  10. Centers for Disease control and prevention. 2014. Thimerosal in Vaccinations.

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