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Should We Worry About Metals in Vaccines?

Here's what you should know about aluminum and mercury when it comes to getting your shots.

This article was first published in The Montreal Gazette.

Last time, we explored a specific concern voiced by a reader — namely, why we vaccinate babies for adult diseases like Hepatitis B. This week, we’ll look at another vaccine question. Why are there metals in vaccines?

You will no doubt have heard that there’s aluminum in vaccines. Aluminum is used as an adjuvant, which means its presence boosts the immune response when you are vaccinated.

You can only become immune to an illness in two ways. The first is to get sick. The bacteria or virus will enter your body, your immune system will identify the infection, fight it off, and produce antibodies to prevent you from ever catching the same disease again. Vaccines are basically pieces of a bacteria or virus that are killed or inactivated in some way. When you get injected with a vaccine, your immune system identifies the virus or bacteria and starts to produce antibodies against it.

In both cases you produce antibodies against the infection, but with vaccines you only have to deal with an inactive fragment and don’t have to go through the full illness.

So where do adjuvants come in? Going as far back as Jonas Salk and his work with the polio vaccine, researchers realized that adjuvants allowed you to use smaller vaccine doses. As a result, although we have more vaccines in total, the amount of antigens (bacteria and viruses) used in vaccines has been decreasing over time. For example, the smallpox vaccine itself had 200 protein antigens in it and the pertussis vaccine used to have about 3,000, although modern vaccines only have about 130 antigens combined.

The point is adjuvants serve an important and critical purpose in vaccines. But is the use of aluminum safe? In fact, aluminum is one of the most common elements in the Earth’s crust and is present in almost all our food. We are all eating aluminum every day. Infants are exposed to more aluminum in breast milk or formula than they are from vaccines, but either way these are tiny doses that don’t have any major health effect.

You might have heard about a U.S. Food and Drug Administration imposed limit of 25 micrograms per day on aluminum. It’s worth noting that this number has to do with total parenteral nutrition (TPN) or feeding through an intravenous. We regularly consume much more aluminum than this in food or breast milk, and vaccines are not IVs. They are injections under the skin, not into the bloodstream. After several decades of use and study, there is no good reason to believe that the small doses of aluminum used in vaccines are dangerous.

The other metal that tends to come up in vaccine discussions is mercury. Vaccines used to contain thimerosal, an organic compound that contains a mercury atom, much like hemoglobin contains iron atoms. Thimerosal is an ethyl mercury compound (mercury attached to two carbon atoms). This is often confused with methyl mercury (mercury attached to one carbon atom). Methyl mercury is what accumulates in water and fish and can cause health problems. Ethyl mercury is a very different compound that doesn’t appear to be toxic. If you want to understand the difference one carbon atom can make, consider the difference between methanol and ethanol. Drinking ethanol (alcohol) will make you tipsy at a dinner party. Drinking methanol can make you go blind.

Thimerosal was used as a preservative to prevent bacterial contamination once a vaccine vial was opened. But the point is somewhat moot now as it has not been used in most vaccines, with the exception of the flu vaccine, since 2001.

There are good reasons not to want (methyl) mercury in our lakes and rivers, because it is toxic to humans. There is no good reason to be worried about ethyl (mercury) in vaccines. Largely because there isn’t any in most of them.


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