The CDC is misleading the public about mercury in vaccines

On the safety of thimerosal

Thimerosal

You may have heard that some vaccines contain thimerosal, a mercury-containing preservative. The use of thimerosal in vaccines has declined in the United States since 2001, but it remains in flu vaccines, as well as many vaccines in developing countries.

It’s also unclear just how much remains in childhood vaccines in the United States; the FDA says that thimerosal-free vaccines are available, but they haven’t said whether all kids are given the thimerosal-free versions. Here’s exactly how they’ve worded their statements on this:

All vaccines routinely recommended for children 6 years of age and younger in the U.S. are available in formulations that do not contain thimerosal.

As with pediatric vaccines, vaccines for adolescents and adults are available in formulations that do not contain thimerosal.

What is clear, is that some childhood vaccines in the U.S., at the very least, still contain trace amounts of thimerosal that were used as a part of their manufacturing processes (examples here and here).

Thimerosal can also be found in all kinds of household products, like cosmetics, eye drops, and nose sprays.

Image from here.

Is thimerosal safe? That’s what we’ll look into here.

What the CDC says about thimerosal safety

Here’s what the CDC says about the safety of thimerosal:

There is no evidence of harm caused by the low doses of thimerosal in vaccines, except for minor reactions like redness and swelling at the injection site.

But thimerosal contains mercury, which is extremely toxic. How could it be ok to inject this into people?

Well, according to the CDC:

Thimerosal contains ethylmercury, which is cleared from the human body more quickly than methylmercury, and is therefore less likely to cause any harm.

And:

Thimerosal does not stay in the body a long time so it does not build up and reach harmful levels. When thimerosal enters the body, it breaks down to ethylmercury and thiosalicylate, which are readily eliminated.

Methylmercury is widely found in the environment, including in fish; it’s the reason why pregnant women are sometimes told to limit their consumption of fish. This is different from ethylmercury, the kind of mercury found in thimerosal. In the image below, methylmercury is on the left and ethylmercury is on the right:

Methylmercury (left) has mercury (Hg) bonded to a “methyl group” which is a carbon bonded to 3 hydrogens. Ethylmercury (right) has mercury that’s bonded to an “ethyl group” which has 2 carbons and 5 hydrogens.

They’re both positively charged ions (cations) that will readily react with other things.¹

This is echoed by people like Paul Offit, widely considered a “vaccine expert”:

Offit says ethylmercury is “a larger molecule and as a consequence is secreted 10x more quickly than is methylmercury.” According to him, this means that methylmercury “accumulates to a far greater extent in the body than ethylmercury” and “parents should be reassured by that.”

In fact, in 2007 Offit expressed that the alarm caused by the removal of thimerosal from vaccines was quite harmful (see here).

The principal arguments

The CDC seems to be making two arguments related to the safety of thimerosal:

1. The kind of mercury found in vaccines, ethylmercury, is “less likely to cause any harm” because it’s “cleared from the human body more quickly than methylmercury,” and “readily eliminated.”

2. There is no evidence of harm caused by the low doses of thimerosal in vaccines.

This article will focus on the first argument. In a future article we will look at the second.

The studies that the CDC cites

What data is the CDC basing argument #1 on?

If we look at the studies that the CDC cites as “thimerosal-related scientific articles” and filter for the ones that pertain to the clearance of mercury in the body after thimerosal injection, we get these three:

Study 1: Pichichero et al. 2002 Mercury concentrations and metabolism in infants receiving vaccines containing thiomersal: a descriptive study

Study 2: Pichichero et al. 2009 Mercury levels in premature and low birth weight newborn infants after receipt of thimerosal-containing vaccines

Study 3: Burbacher et al. 2005 Comparison of Blood and Brain Mercury Levels in Infant Monkeys Exposed to Methylmercury or Vaccines Containing Thimerosal

Two of these three studies are also cited by the World Health Organization.

Let’s see if the findings of these studies are reassuring.

Study 1

The first study (Pichichero et al. 2002) looked at blood, urine, and stool samples from babies at various time points after they’d been given thimerosal-containing vaccines. They were compared to babies who had not been given thimerosal.

The authors of the study estimated that the half-life of blood mercury, aka the length of time it takes to get rid of half the mercury in the blood, was about 7 days.

The authors stated that blood concentrations were not “above safe values in infants.” Specifically, “no children had a concentration of blood mercury exceeding 29 nmol/L which is the concentration thought to be safe in cord blood.”

However, that conclusion was contested in this correspondence in The Lancet:

However, the authors did not measure the peak blood concentrations that occurred within hours after the injections…

The data are available for one child in their study: a 2-month-old with a blood mercury concentration of 20·55 nmol/L 5 days after vaccination. If the ethylmercury half-life is 7 days (and half lives are variable), the peak mercury concentration in blood would have been 29·4 nmol/L, which is right at the safety level.

This leaves no margin of safety if there were other sources of mercury exposure as well, belying the authors' claim that “no children had a concentration of blood mercury exceeding 29 nmol/L”.

This study also found that babies given thimerosal had undetectable levels of mercury in their urine, and between 23-141 ng mercury per gram of stool.

The authors reported this as evidence that the infants were successfully eliminating mercury in the stool, but these concentrations were very low compared to the amount of mercury they were given. According to this calculation, for those infants excreting mercury at the lower end of the range (23 ng/gram of stool), it would take roughly four years to get rid of all the mercury given by the vaccines.

Study 2

The second study (Pichichero et al. 2009), by the same author, also looked at mercury in the blood, stool, and urine from babies at various time points after they’d been given thimerosal-containing vaccines. Similar to Study 1, they estimated that the half-life of blood mercury was about 6.3 days, and blood mercury levels had returned to pre-vaccination levels by day 30.

Conflicts of interest

It should be mentioned that the lead author of both of these studies, Michael Pichichero, helped to develop several vaccines, and received grants and/or honoraria from Pfizer, Eli Lilly, Bristol-Myers Squibb, and other vaccine makers.

He did not declare his financial conflicts of interest in his paper.

Screenshot from the Pichichero et al. 2002 paper

What happens in the blood is not indicative of what happens in the organs

Now, according to both these studies, blood mercury levels decreased by half in about a week, but this was just in the blood. It doesn’t show us anything about how much mercury got into organs, and whether mercury in those organs had a similar half-life.

They also did not do a “mass balance” calculation whereby they took the total amount of ethylmercury the babies were given from the vaccines, and measured how long it took for all that mercury to exit the body, whether via the stools, urine, skin, or hair.

The first study said, “blood mercury concentrations indicate concentrations in organs well,” but even one of the studies that the CDC sites, Burbacher et al. 2005, shows that this is not the case. We’ll look at that study next.

Study 3

Study 3 (Burbacher et al. 2005) looked at infant monkeys that were given either methylmercury or thimerosal, in dosages that were comparable to the immunization schedule for human newborns at the time. They looked at mercury levels in the blood and brain at various timepoints after last mercury exposure.

They found mercury in the brain in both thimerosal and methylmercury-exposed monkeys. This finding was not mentioned on the CDC site, despite the fact that it came from a study that was cited by the CDC.

The brain concentrations of mercury were about 3-fold lower in the thimerosal-exposed monkeys compared to the ones given methylmercury. However, methylmercury was given orally, while ethylmercury was injected, and according to this study, methylmercury given orally, surprisingly, results in significantly greater concentrations of total mercury in blood and organs compared to injection. So to some extent, this limits direct comparisons.

Anyway, consistent with the other 2 studies, Study 3 found that the half-life of thimerosal-derived mercury was about 6.9 days in the blood. This was shorter than what they found for methylmercury in the blood, which was 19.1 days.

However, mercury in the brain took longer to clear. Although thimerosal-derived mercury cleared faster in the brain than methylmercury-derived mercury in the brain, they estimated that the half-life of thimerosal-derived mercury in the brain was about 24.4 days, which is longer than the half-life for methylmercury in the blood (19.1 days).

Here’s a graph showing total mercury in the brain (black dots) and blood (blue dots) after thimerosal injection:

Significant levels of mercury still remained in the brain at the last time point measured (day 28 after the last injection of thimerosal).

The authors stated:

Data from the present study support the prediction that, although little accumulation of Hg in the blood occurs over time with repeated vaccinations, accumulation of Hg in the brain of infants will occur.

Thus, conclusion regarding the safety of thimerosal drawn from blood Hg clearance data in human infants receiving vaccines may not be valid, given the significantly slower half-life of Hg in the brain as observed in the infant macaques.

“Hg” is the symbol for mercury.

In other words, accumulation of mercury in the brain will probably occur, especially with repeated vaccinations, and blood mercury concentrations are not a good measure of brain mercury levels.

Some ethylmercury gets converted into inorganic mercury, which takes especially long to clear from the brain

Study 3 also found that a significant proportion of ethylmercury gets converted into inorganic mercury, which is mercury that’s part of a compound that does not contain carbon.

This is problematic, because inorganic mercury takes even longer to clear from the brain than both ethylmercury and methylmercury.

The following graph shows the brain levels of both inorganic mercury and organic mercury (which includes ethylmercury and methylmercury), after thimerosal injection:

In the graph, the inorganic mercury concentrations are represented by the blue diamonds. Note that the levels remained virtually unchanged during the course of the study. The authors stated that “The half-life of inorganic Hg is too long (> 120 days) to be accurately estimated from the present data.”

They also cited a study that looked at inorganic mercury in the brains of monkeys over longer time scales.² They found that the half-life of inorganic mercury “was extremely long, 230-540 days in most brain sites and considerably longer in the thalamus and pituitary.” This study stated that the the half-life of inorganic mercury “was extremely long, on the order of years.”

So although some of ethylmercury in the brain gets cleared on the order of days or weeks after thimerosal injection, a significant proportion of that mercury will get converted into an inorganic form that could remain for years.

Meanwhile, reminder that this is what the CDC said on their website:

Technically it’s true that thimerosal “breaks down,” but the fact that a significant proportion of it breaks down into inorganic mercury compounds that can take years to clear from the brain, is not exactly reassuring.

Some ethylmercury also gets converted to methylmercury

By the way, ethylmercury in the body can also break down into methylmercury, according to this study from 2010: Identification and distribution of mercury species in rat tissues following administration of thimerosal or methylmercury

Here’s a table that shows the kinds of mercury-containing compounds in rat tissues, five days after they were given either methylmercury or thimerosal:

“Ino-Hg” is inorganic mercury. “Met-Hg” is methylmercury and “Et-Hg” is ethylmercury.

As you can see, some of the ethylmercury from thimerosal converted to methylmercury or inorganic mercury. The percentages differed between different tissues.

If we look at the the brain five days after thimerosal exposure (circled in red), we can see that 62.8% was inorganic mercury, 23.7% was methylmercury, and 13.5% was ethylmercury.

Also notice how high the mercury levels were in the kidneys after thimerosal injection (circled in blue), especially in the form of inorganic mercury. More on that here: Thimerosal in childhood vaccines contributes to accumulating mercury toxicity in the kidney

Summary of findings

• The CDC says that the kind of mercury found in thimerosal, ethylmercury, is cleared from the human body more quickly than methylmercury, and is therefore less likely to cause any harm.

• The CDC cites papers that estimate that the half life of thimerosal-derived mercury in the blood is about a week.

• Two of the papers that the CDC cites on its website were by an author (Pichichero) who had conflicts of interest.

• But even if we took the results of those studies at face value, they only looked at mercury in the blood. They didn’t show what happened in organs.

• The authors of the studies claimed that blood concentrations were not “above safe values in infants,” but they did not take measurements at timepoints when the mercury blood concentrations likely peaked.

• The levels of mercury excreted by the thimerosal-injected babies were low compared to the total mercury given from vaccines, which implies that the babies were slow to clear the mercury from their bodies. By one estimate, some infants excreting mercury at the lower range of the measurements would take nearly four years to get rid of all the mercury they were given by their vaccines.

• One of the papers that the CDC cites (Burbacher et al. 2005) looked at blood and brain levels of mercury in infant monkeys given methylmercury or thimerosal. They found mercury in the brain in both thimerosal and methylmercury-exposed monkeys. This was never mentioned on the CDC site.

• The mercury levels were about 3-fold lower in the thimerosal-exposed monkeys compared to the methylmercury-exposed monkeys. However, methylmercury was given orally, while ethylmercury was injected, and according to this study, methylmercury given orally results in significantly greater concentrations of total mercury in blood and organs compared to injection; this complicates direct comparisons.

• The Burbacher study concluded that the estimated half-life of ethylmercury in the brain was about 24.4 days, which is longer than the half-life for methylmercury in the blood (about 19.1 days).

• The authors of that study wrote that “data from the present study support the prediction that, although little accumulation of Hg in the blood occurs over time with repeated vaccinations, accumulation of Hg in the brain of infants will occur” (“Hg” is the symbol for mercury).

• That study also found that a significant proportion of ethylmercury gets converted into inorganic mercury, which takes even longer to clear from the brain than either ethylmercury or methylmercury. The levels of inorganic mercury remained virtually unchanged during the course of the study. They stated that “the half-life of inorganic Hg is too long (> 120 days) to be accurately estimated from the present data.”

• What we do know is that according to this study, the half-life of inorganic mercury in the brain “was extremely long, 230-540 days in most brain sites and considerably longer in the thalamus and pituitary.” This study estimated that the the half-life of inorganic mercury “was extremely long, on the order of years.”

• Some of the ethylmercury can also get converted into methylmercury. In the brains of rats five days after thimerosal injection, 23.7% of the total mercury was in the form of methylmercury.

• It should also be mentioned that the half-lives of all species of mercury were all estimates. In all of these studies, they just took several time points and extrapolated half-lives, using models.

• It should also be mentioned that what we know about how mercury clears from the brain is mostly based on animal models like monkeys and rodents. Results from these studies might not be representative of what happens in humans.

Based on this, do you agree with Paul Offit that “parents should be reassured”?

When the CDC states on its website that “thimerosal does not stay in the body a long time so it does not build up and reach harmful levels,” are they being completely forthright and transparent?

In a future article, we will look at the CDC claim that “there is no evidence of harm caused by the low doses of thimerosal in vaccines.”

Stay tuned.

1. They can combine with negatively charged ions like chloride (Cl⁻) or hydroxide (OH⁻) or compounds that contain sulfur (thiols), for example. Often when people say “methylmercury” or “ethylmercury” they mean compounds that contain methylmercury or ethylmercury respectively, combined with other things.

2. It should be mentioned that this study looked at inorganic mercury that had originally derived from methylmercury (specifically demethylation of methylmercury). Similar processes seem to be happening with ethylmercury whereby some ethylmercury gets converted to methylmercury and/or inorganic mercury.