Is it Safe

Q: Flu season is approaching and I heard that shots still contain mercury. Is that true? Should I get a flu shot if I am pregnant?

A: You raise an important question that became controversial a decade ago when it became common knowledge that many vaccines contained thimerosal as a preservative.

Thiomerosal is a mercury-based preservative. The FDA acted quickly to get thimerosal out of vaccines intended for children under 6 years of age although there was never proof that this preservative actually harmed children. For example, the studies on vaccines and autism have not shown a correlation (autism rates continue to go up even after thimerosal was removed from childhood vaccines).

However, it is still in some versions of the flu shot, specifically those that come in multi-use vials, that is vials which contain many doses. Single use vials of the flu vaccine do not contain mercury. So, if you want to avoid the mercury preservative you could ask whether the doctor or clinic is using single or multi-use vials and try to opt for a facility using the single use vials. From a toxicology perspective that is not really necessary.

The amount of mercury in a flu shot from a multi-use vial is only 25 micrograms, roughly the equivalent amount of mercury from a can of tuna fish. And you are only getting vaccinated once a year so for most people the exposure from the vaccine is minor compared to mercury exposure from fish in your diet. That is why public health efforts focus on providing advice about fish consumption as some fish are high in mercury (e.g., swordfish and shark) while other types of fish are low (e.g., salmon, cod and flounder). Getting back to your initial question, don’t worry about the mercury content in the flu vaccine, even if you are pregnant. Pregnant woman can eat tuna fish during pregnancy, one to two meals per week, so one flu shot will not add much to what is considered a safe amount of mercury from fish ingestion.

Further, it is vitally important for pregnant women to not get the flu so the benefits of the flu shot clearly outweigh the small dose of mercury that might be encountered in the flu shot.

******
Dr. Gary Ginsberg is a public health toxicologist in Connecticut and a lecturer at the Yale School of Public Health. He has written a book geared toward the general public, “What’s Toxic, What's Not,” and also has a website, whatstoxic.com, to answer questions about chemicals found in consumer products and in our homes.

******
The Yale School of Public Health invites you to submit questions for Dr. Ginsberg as part of this recurring monthly series. Contact us through Facebook or by e-mailing Michael Greenwood at michael.greenwood@yale.edu